Scalable virtual traffic hub interconnecting isolated networks

ABSTRACT

Metadata indicating that an action implementation node and a routing decision master node have been assigned to a virtual traffic hub programmatically associated with one or more isolated networks is stored. The routing decision master node determines a first action to be implemented for packets of a network flow using state information of the isolated networks, and provides a representation of a first action to the first action implementation node. Based on performing the first action at the action implementation node, contents of a data packet received from one isolated network are transmitted to another isolated network.

BACKGROUND

Many companies and other organizations operate computer networks thatinterconnect numerous computing systems to support their operations,such as with the computing systems being co-located (e.g., as part of alocal network) or instead located in multiple distinct geographicallocations (e.g., connected via one or more private or publicintermediate networks). For example, data centers housing significantnumbers of interconnected computing systems have become commonplace,such as private data centers that are operated by and on behalf of asingle organization, and public data centers that are operated byentities as businesses to provide computing resources to customers. Somepublic data center operators provide network access, power, and secureinstallation facilities for hardware owned by various customers, whileother public data center operators provide “full service” facilitiesthat also include hardware resources made available for use by theircustomers.

The advent of virtualization technologies for commodity hardware hasprovided benefits with respect to managing large-scale computingresources for many customers with diverse needs, allowing variouscomputing resources to be efficiently and securely shared by multiplecustomers. For example, virtualization technologies may allow a singlephysical virtualization host to be shared among multiple users byproviding each user with one or more “guest” virtual machines hosted bythe single virtualization host. Each such virtual machine may representa software simulation acting as a distinct logical computing system thatprovides users with the illusion that they are the sole operators of agiven hardware computing resource, while also providing applicationisolation and security among the various virtual machines. Instantiatingseveral different virtual machines on the same host may also helpincrease the overall hardware utilization levels at a data center,leading to higher returns on investment.

As demand for virtualization-based services at provider networks hasgrown, more and more networking and interconnectivity-related featuresmay have to be added to meet the requirements of applications beingimplemented using the services. Many such features may require networkpacket address manipulation in one form or another, e.g., at level 3 orlevel 4 of the open systems interconnect stack. Some clients ofvirtualized computing services may wish to employ customizedpolicy-based packet processing for application traffic flowing betweenspecific sets of endpoints. Using ad-hoc solutions for all the differenttypes of packet transformation requirements may not scale in largeprovider networks at which the traffic associated with hundreds ofthousands of virtual or physical machines may be processed concurrently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example system environment comprising resources ofa scalable cell-based packet processing service at whichclient-specified forwarding metadata and policies may be used toimplement a variety of networking applications, according to at leastsome embodiments.

FIG. 2 illustrates a high-level overview of example interactions amongcomponents of an isolated cell designated for a particular applicationat a packet processing service, according to at least some embodiments.

FIG. 3 illustrates an example scenario in which an isolated packetprocessing cell may comprise nodes distributed among multipleavailability containers of a virtualized computing service, according toat least some embodiments.

FIG. 4 illustrates an example use of multiplexed virtual networkinterfaces for communications between isolated networks and a packetprocessing service, according to at least some embodiments.

FIG. 5 illustrates example packet flow identifier elements and examplepacket processing policy elements, according to at least someembodiments.

FIG. 6 illustrates example categories of packet processing applicationsthat may be implemented using a cell-based packet processing service,according to at least some embodiments.

FIG. 7 illustrates example configuration parameters of a cell of apacket processing service, according to at least some embodiments.

FIG. 8, FIG. 9, FIG. 10 and FIG. 11 collectively illustrate an exampletechnique for migrating traffic of an application between cells of apacket processing service, according to at least some embodiments.

FIG. 12 illustrates example control-plane elements of a packetprocessing service, according to at least some embodiments.

FIG. 13 illustrates example pathways of health-related messages amongnodes of an isolated packet processing cell, according to at least someembodiments.

FIG. 14 illustrates an example technique which may be employed to gatherhealth information within an action implementation node of a packetprocessing service, according to at least some embodiments.

FIG. 15 is a flow diagram illustrating aspects of operations that may beperformed to implement a multi-layer cell-based packet processingservice, according to at least some embodiments.

FIG. 16 illustrates an example system environment in which a virtualtraffic hub for managing the flow of traffic between isolated networksusing a cell-based packet processing service may be implemented,according to at least some embodiments.

FIG. 17 illustrates examples of packet data paths between isolatednetworks connected via a virtual traffic hub, as viewed from a customerperspective and as implemented using a packet processing service,according to at least some embodiments.

FIG. 18 illustrates an example of the management of virtual traffichub-related packet processing workloads at an action implementation nodeof a packet processing service, according to at least some embodiments.

FIG. 19 illustrates an example of the management of virtual traffichub-related packet processing workloads at a decision master node of apacket processing service, according to at least some embodiments.

FIG. 20 illustrates an example of a sequence of interactions between anaction implementation node and a decision master node, according to atleast some embodiments.

FIG. 21, FIG. 22 and FIG. 23 collectively illustrate an example of thecreation and use of filtered route tables at decision master nodesdesignated for a virtual traffic hub, according to at least someembodiments.

FIG. 24 illustrates example virtual traffic hub-related control planeprogrammatic interactions between a client and a packet processingservice, according to at least some embodiments.

FIG. 25 illustrates an example scenario in which multiple virtualtraffic hubs may be programmatically linked to one another, according toat least some embodiments.

FIG. 26 is a flow diagram illustrating aspects of operations that may beperformed to route traffic between isolated networks using a virtualtraffic hub that utilizes resources of a packet processing service,according to at least some embodiments.

FIG. 27 illustrates an example system environment in which a virtualtraffic hub may be used to connect isolated networks which may haveoverlapping network address ranges, according to at least someembodiments.

FIG. 28 and FIG. 29 collectively illustrate examples of alternativeapproaches for detecting and responding to overlapping address rangesamong isolated networks connected via a virtual traffic hub, accordingto at least some embodiments.

FIG. 30 is a flow diagram illustrating aspects of operations that may beperformed to route traffic between isolated networks using a virtualtraffic hub, in scenarios in which the isolated networks may haveoverlapping address ranges, according to at least some embodiments.

FIG. 31 illustrates an example system environment in which a virtualtraffic hub may be used to automatically propagate routing informationamong isolated networks, according to at least some embodiments.

FIG. 32 illustrates examples of triggering events that may lead to thepropagation of routing information by a virtual traffic hub to one ormore isolated networks, according to at least some embodiments.

FIG. 33 illustrates examples of a domain-restricted propagation ofrouting information by a virtual traffic hub, according to at least someembodiments.

FIG. 34 illustrates an example of the use of an address translationmapping during the propagation of routing information by a virtualtraffic hub, according to at least some embodiments.

FIG. 35 is a flow diagram illustrating aspects of operations that may beperformed at a virtual traffic hub to propagate routing informationbetween isolated networks, according to at least some embodiments.

FIG. 36 illustrates an example system environment in which a virtualtraffic hub may participate in the distribution of Domain Name System(DNS) information to resources of isolated networks, according to atleast some embodiments.

FIG. 37 illustrates examples of programmatic interactions between aclient and a packet processing network at which a virtual traffic hubmay be used to perform DNS-related operations, according to at leastsome embodiments.

FIG. 38 illustrates an example use of a virtual traffic hub to provideDNS information to isolated networks within and outside a providernetwork, according to at least some embodiments.

FIG. 39 is a flow diagram illustrating aspects of operations that may beperformed at a virtual traffic hub to propagate DNS information toresources at isolated networks, according to at least some embodiments.

FIG. 40 is a block diagram illustrating an example computing device thatmay be used in at least some embodiments.

While embodiments are described herein by way of example for severalembodiments and illustrative drawings, those skilled in the art willrecognize that embodiments are not limited to the embodiments ordrawings described. It should be understood, that the drawings anddetailed description thereto are not intended to limit embodiments tothe particular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope as defined by the appended claims. The headings usedherein are for organizational purposes only and are not meant to be usedto limit the scope of the description or the claims. As used throughoutthis application, the word “may” is used in a permissive sense (i.e.,meaning having the potential to), rather than the mandatory sense (i.e.,meaning must). Similarly, the words “include,” “including,” and“includes” mean including, but not limited to. When used in the claims,the term “or” is used as an inclusive or and not as an exclusive or. Forexample, the phrase “at least one of x, y, or z” means any one of x, y,and z, as well as any combination thereof.

DETAILED DESCRIPTION

Various embodiments of methods and apparatus for implementing amulti-layer packet processing service comprising a plurality oflogically isolated cells, and utilizing the service to build a number ofhigher level applications such as virtual traffic hubs are described.Such a service may comprise two broad categories of resources in atleast some embodiments: control plane resources, and data planeresources. The control plane may comprise resources that are primarilyresponsible for administrative tasks such as setting up the initialservice resource configurations for various networking applications,monitoring the configurations, modifying the configurations if needed,and so on. In contrast, the data plane may be responsible forimplementing the processing of application packets based on guidelinesindicated by clients of the packet processing service, and transferringcontents of such packets between endpoints associated with theapplications that have been set up on behalf of the clients. In at leastsome embodiments, a set of data plane nodes and control plane nodes ofthe packet processing service, where individual ones of the nodes may beimplemented using one or more computing devices, may be grouped togetherto form an isolated packet processing cell (IPPC), and at least one suchcell may be assigned to implement a given instance of an application.One such application may, for example, comprise a virtual traffic hub(e.g., a transit gateway) that can be used to (among other functions)route traffic between isolated networks (e.g., virtual networks hostedby a service provider, where the service provider operates a substratenetwork and virtualizes the Internet Protocol (IP) space made availableto resources in the virtual network, networks whose resources may beassigned private Internet Protocol (IP) addresses that are notadvertised outside the networks, etc.). In an example embodiment,customers of the service provider can use virtual traffic hubs tocentrally manage the interconnectivity of isolated networks andon-premises networks. In an embodiment, multiple virtual traffic hubsmay be established, e.g., based on requests received at the packetprocessing service from different customers with their respectiveconnectivity needs, and each such hub may represent an instance of thevirtual traffic hub application and be assigned a respective IPPC.Another example of an application to which one or more cells may beassigned may involve multicasting individual packets from some set ofsource endpoints to a plurality of destination endpoints in someembodiments.

A given cell of the packet processing service may be referred to in someembodiments as being “isolated” because, at least during normaloperating conditions, no data plane network traffic may be expected toflow from that cell to any other cell of the service. In at least oneembodiment, control plane traffic may also not flow across cellboundaries under normal operating conditions. As a result of suchisolation, a number of benefits may be obtained: e.g., (a) an increasein a workload of one instance of a packet processing application, beingimplemented using one cell, may have no impact on the resources beingused for other applications at other cells, and (b) in the rare eventthat a failure occurs within a given cell, that failure may not beexpected to have any impact on applications to which other cells havebeen assigned. Software updates may be applied to nodes of one cell at atime, so any bugs potentially introduced from such updates may notaffect applications using other cells. The specific type of packetprocessing being performed may vary from one application to another, andas a result from one cell to another in at least some embodiments. Insome embodiments, while at least one isolated packet processing cell maybe assigned to a given application instance, a given cell maypotentially be employed in a multi-tenant mode for multiple applicationinstances configured on behalf of multiple customers. In at least someembodiments, nodes of the packet processing service cells may generateand run highly efficient executable programs to implement theapplication-specific packet processing logic based on customer-suppliedpolicies, e.g., using a virtual machine instruction set optimized fornetworking-related operations.

As one skilled in the art will appreciate in light of this disclosure,certain embodiments may be capable of achieving various advantages,including some or all of the following: (a) enabling a wide variety ofclient-selected customized packet processing operations (e.g.,associated with Layer 3 of the Internet networking protocol stack or itsequivalent in other protocol stacks) to be implemented efficiently,thereby reducing the overall CPU load associated with the packetprocessing, (b) improving the overall responsiveness of applicationsthat utilize the packet processing operations, e.g., by adding packetprocessing resources as the application workload increases, (c)enhancing the security of networking applications by isolating the setof resources utilized for a given instance of an application, and/or (d)enhancing the user experience of system administrators and/orapplication owners by providing configuration information and metricsseparately on a per-application-instance level. The amount of computingand other resources needed to deal with scenarios such as possibleoverlaps among private address ranges used in different isolatednetworks, the propagating of route changes from one isolated network toanother, and/or the propagation of DNS information to resources withinisolated networks may also be reduced in at least some embodiments.

According to some embodiments, a system may comprise a set of computingdevices of a packet processing service. The computing devices mayinclude instructions that upon execution on a processor cause thecomputing devices to assign, to a first application with a first set ofsource endpoints and a second set of destination endpoints, a firstisolated packet processing cell (IPPC) of a plurality of isolated packetprocessing cells of the packet processing service. The IPPC maycomprise, for example, (a) a plurality of action implementation nodes(AINs), (b) one or more decision master nodes (DMNs), and (c) one ormore administration or control plane nodes (ANs) in at least oneembodiment. In some embodiments, at least a first AIN of the IPPC mayhave a programmatically attached virtual network interface (VNI)configured to receive network traffic originating at one or more of thesource endpoints, and at least a second AIN of the IPPC may have aprogrammatically attached VNI enabling transmission of traffic along apath to one or more of the destination endpoints. A VNI, as suggested bythe name, may in various embodiments comprise a set of networkingconfiguration settings (such as one or more IP addresses, security rulesand the like) that can be programmatically associated with executionplatforms such as virtual machines, and potentially programmaticallytransferred from one platform to another to enable the configurationsettings to be used to transmit and receive network traffic overdifferent physical network interfaces. In some cases, a given AIN may beconnected (e.g., using one or more VNIs) to one or more sources as wellas destinations of the application traffic. An application isolationpolicy of the packet processing service may prohibit transmission of atleast some types of network packets between the first IPPC and otherIPPCs in various embodiments. In at least some implementations, networkconfiguration settings (e.g., security-related settings of one or moreVNIs used for communicating with/among IPPC nodes, or routing tableentries used within the IPPCs) may prohibit/prevent the transmission ofsome types of messages (e.g., data plane packets) across IPPCboundaries. For example, a given DMN may be configured to providerepresentations of actions only to AINs of its own IPPC, and not to AINsin other IPPCs in various embodiments.

An indication of a collection of packet forwarding metadata of the firstapplication, such as entries of a forwarding information base, may bereceived via a programmatic interface from a client of the packetprocessing service, and the collection may be propagated to the DMNs invarious embodiments. Such forwarding metadata may represent one exampleof decision metadata that be employed to make decisions regardingactions at the DMNs in various embodiments. An action query may bereceived at a DMN from the first AIN, e.g., as a result of a cache missin a local action cache accessible at the first AIN when an attempt ismade to find an action corresponding to a packet received from a firstsource endpoint in some embodiments. From the DMN, in response to theaction query, a representation of a packet processing action to beimplemented with respect to a group of one or more packets may beprovided to the first AIN. The group of packets may include the packetthat led to the cache miss and the action query, as well as otherpackets of the same flow in some embodiments, where one flow may bedistinguished from other flows by a combination of header entry valuesand/or other properties. As such, the action may be cached at the firstAIN and potentially re-used later, if/when other packets of the groupare received. The action determined at the DMN may be based at least inpart on the packet forwarding metadata and a packet processing policyindicated by the client or customer on whose behalf the first IPPC isconfigured in at least some embodiments. At the first AIN, the actionmay be performed with respect to the packet received from the sourceendpoint; as a result, at least one outbound (with respect to the packetprocessing service) packet may be transmitted along a path to adestination endpoint. In some cases, the outbound packet may betransmitted via the second AIN—that is, not all the AINs may haveconnectivity to all the source or destination endpoints. In other cases,the outbound packet may not have to be transmitted via a path thatincludes other endpoints.

The administration nodes of the IPPC may monitor various metricsassociated with the AINs and the DMNs in some embodiments, and initiatecell reconfiguration operations as and when needed based on resourcemanagement policies being enforced for at least the first IPPC invarious embodiments. The reconfiguration operations may include, forexample, adding AINs/DMNs, removing/decommissioning AINs/DMNs, settingup additional virtual network interfaces, and the like. In someembodiments, e.g., in which the nodes of the IPPC are being used inmulti-tenant mode, an application's traffic may be transferred ormigrated from one IPPC to another under some conditions, e.g., based onmetrics gathered at the administration nodes. A multi-phase migrationtechnique that avoids transferring data plane traffic across thepre-migration IPPC and the post-migration IPPC may be employed in someembodiments.

A given IPPC may be assigned to multiple applications of one or moreclients of the packet processing service in some embodiments, e.g.,resulting in respective sets of actions being generated (at the DMNs)and executed (at the AINs) for the different applications, in accordancewith policies and metadata provided by the clients for the applications.The multiple applications to which a given IPPC is assigned may beinstances of the same type of application (e.g., virtual routingapplications, providing routing between different groups of isolatednetworks), or instances of different networking application categories(e.g., both a virtual routing application and a multicast applicationmay be implemented using a given cell).

In at least some embodiments, a shuffle sharding algorithm may be usedto assign a subset of nodes (e.g., AINs) of an IPPC to a given set ofone or more source or destination endpoints of a given application.According to such an algorithm, if the IPPC comprises N AINs, packetsfrom a given source endpoint E1 may be directed (e.g., based on hashingof packet header values) to one of a subset S1 of K AINs (K<N), andpackets from another source endpoint E2 may be directed to anothersubset S2 of K AINs, where the maximum overlap among S1 and S2 islimited to L common AINs. Similar parameters may be used forconnectivity for outbound packets to destination endpoints from thepacket processing service in various embodiments. Such shuffle shardingtechniques may combine the advantages of hashing based load balancingwith higher availability for the traffic of individual ones of thesource and destination endpoints in at least some embodiments.

In various embodiments, the packet processing service may be implementedat least in part using resources of a provider network. Networks set upby an entity such as a company or a public sector organization toprovide one or more network-accessible services (such as various typesof cloud-based computing, storage or analytics services) accessible viathe Internet and/or other networks to a distributed set of clients maybe termed provider networks in one or more embodiments. A providernetwork may sometimes be referred to as a “public cloud” environment.The resources of a provider network may in some cases be distributedacross multiple data centers, which in turn may be distributed amongnumerous geographical regions (e.g., with each region corresponding toone or more cities, states or countries). In one embodiment, each regionmay include one or more availability containers, which may also betermed “availability zones”. An availability container in turn maycomprise portions or all of one or more distinct locations or datacenters, engineered in such a way (e.g., with independent infrastructurecomponents such as power-related equipment, cooling equipment, orphysical security components) that the resources in a given availabilitycontainer are insulated from failures in other availability containers.A failure in one availability container may not be expected to result ina failure in any other availability container; thus, the availabilityprofile of a given resource is intended to be independent of theavailability profile of resources in a different availability container.Various types of services, including for example a packet processingservice of the kind introduced above, may therefore be protected fromfailures at a single location by launching multiple resources on behalfof a given application in respective availability containers, or (in thecase of a packet processing service) distributing the nodes of a givencell across multiple availability containers. Thus, for example, in someembodiments at least one AIN of a given IPPC may be established withineach of at least two availability containers, and similarly, respectiveDMNs and administration nodes (ANs) of the IPPC may also be establishedin more than one availability container.

In some embodiments, at least some nodes (e.g., AINs, DMNs and/or ANs)of at least some IPPCs may be implemented using virtual machines, e.g.,instantiated on hosts of a virtualized computing service (VCS) of aprovider network. In other embodiments, physical machines that do notimplement virtualization may be used for at least some nodes of a packetprocessing service. In one embodiment, respective isolated virtualnetworks (IVNs) may be established on behalf of various clients at theVCS. An isolated virtual network may comprise a collection of networkedresources (including, for example, virtual machines) allocated to agiven client, which are logically isolated from (and by default,inaccessible from) resources allocated for other clients in otherisolated virtual networks. The client on whose behalf an IVN isestablished may be granted substantial flexibility regarding networkconfiguration for the resources of the IVN—e.g., private IP addressesfor virtual machines may be selected by the client without having toconsider the possibility that other resources within other IVNs may havebeen assigned the same IP addresses, subnets of the client's choice maybe established within the IVN, security rules may be set up by theclient for incoming and outgoing traffic with respect to the IVN, and soon. In at least one embodiment, a given IPPC may be implemented usingone or more IVNs. In some embodiments in which the packet processingservice is being used for routing traffic among isolated networks, theisolated networks themselves may comprise one or more IVNs of a VCS.

A number of programmatic interfaces, such as a set of applicationprogramming interfaces (APIs), a web-based console, command-line toolsand the like may be implemented by the packet processing service invarious embodiments, enabling clients to submit requests and receiveresponses pertaining to their networking applications. A wide variety ofAPIs may be supported in some embodiments, e.g., including APIs toregister or create a new application instance such as a virtual routerhub, to associated virtual network interfaces (VNIs) with applicationsand IPPCs, to submit routing/forwarding metadata and policies, and thelike. In at least some embodiments, VNIs may be configured in amultiplexed manner, in which for example a “trunk” VNI is attached to anAIN and configured to receive packets from (or send packets to) multiplenetwork endpoints accessible from isolated networks whose packets are tobe processed at the service.

Example System Environment

FIG. 1 illustrates an example system environment comprising resources ofa scalable cell-based packet processing service at whichclient-specified forwarding metadata and policies may be used toimplement a variety of networking applications, according to at leastsome embodiments. As shown, system 100 comprises various layers of alayer-3 packet processing service (PPS) 102, including an actionimplementation layer 142, a decisions layer 142 and a celladministration layer 143, as well as a set of service-levelcontrol-plane resources 170 including API handlers, metadatastores/repositories and the like in the depicted embodiment. Individualones of the layers 141, 142 and 143 may comprise a plurality of nodes,such as action implementation nodes (AINs) at layer 141, decision masternodes (DMNs) at layer 142, and administration nodes (ANs) at layer 142.Resources of layers 141, 142, 143 may be organized into groups calledisolated packet processing cells (IPPCs) 127 (e.g., 127A or 127) invarious embodiments, with a given IPPC 127 comprising some number ofAINs, some number of DMNs, and some number of ANs. For example, IPPC127A may include AINs 120A, 120B and 120C, DMNs 122A and 122B, and ANs125A and 125B in the depicted embodiment, while IPPC 127B may compriseAINs 120L, 120M and 120N, DMNs 122C and 122D, and ANs 125J and 125K.Individual nodes such AINs, DMNs and/or ANs may be implemented usingsome combination of software and hardware at one or more computingdevices in different embodiments—e.g., in some embodiments, a given AIN,DMN or AN may comprise a virtual machine running at a host managed by avirtualized computing service, while in other embodiments AINs, DMNsand/or ANs may be implemented using non-virtualized servers.

The resources of the packet processing service 102 may serve as aninfrastructure or framework that can be used to build a variety ofnetworking applications, such as applications for forwarding/routingpackets between isolated networks, applications for multicastingpackets, virtual private networking applications and the like indifferent embodiments. Individual IPPCs 127 may be assigned to implementthe logic of one or more instances of such an application in someembodiments, with the traffic associated with that application beingprocessed (at least under normal operating conditions) without crossingIPPC boundaries. For example, in the depicted embodiment, IPPC 127A hasbeen assigned to an application for transmitting packets between atleast isolated network 110A and isolated network 110B, while IPPC 127Bhas been assigned for transmitting packets between at least isolatednetwork 110J and 110K. Individual ones of the isolated networks 110 mayhave associated private IP address ranges, such that addresses assignedto resources within a given isolated network 110 may not be visible toresources outside the isolated network, and such that at least bydefault (e.g., prior to the assignment of an IPPC implementing a virtualrouting application), a pathway between resources within differentisolated networks may not necessarily be available.

In various embodiments, instances of networking applications, such asvirtual traffic hubs that perform routing between isolated networks 110,may be set up in response to programmatic requests received fromcustomers of the PPS 102. Such requests may, for example, be received atAPI handlers of the PPS control-plane 170. In response to a client'srequest or requests to enable virtualized routing via a hub betweenisolated networks 110A and 110B, for example, IPCC 127A may be assignedto forward packets among the two isolated networks in the depictedembodiment. Similarly, in response to another client's request (or thesame client's request) to enable multicast connectivity among isolatednetworks 110J, 110K and 110L, IPPC 127B may be assigned. In at leastsome embodiments, as discussed below in further detail, a collection ofvirtual network interfaces may be programmatically configured to enabletraffic to flow between endpoints (TEs 112, such as 112D, 112E, 112J,112K, 112P, 112Q, 112R, 112S, 112V and 112W) in the isolated networksand the AINs of the cell assigned to those isolated networks. Clients onwhose behalf the networking applications are being configured mayprovide decision metadata (e.g., layer 3 metadata 123 such as forwardinginformation base entries, routing information base entries and the like)and/or policies that can be used to determine the packet processingactions that are to be performed via control plane programmaticinterfaces of the PPS in some embodiments. The metadata received fromthe clients may be propagated to the decision manager nodes of theappropriate IPPCs 127, e.g., from the PPS API handlers via the ANs 125or directly in the depicted embodiment. In at least some embodiments,the metadata initially provided by the clients may be transformed, e.g.,by converting high-level routing/forwarding entries into more concreteentries that take into account the identifiers of virtual networkinterfaces to be used, locality-related information, information aboutthe availability containers in which various AINs are configured, and soon, and the transformed versions may be stored at the different DMNs 122as discussed below in further detail.

A given packet from a source endpoint such as TE 112K of isolatednetwork 110A may be received at a particular AIN such as 120C in thedepicted embodiment. The specific AIN to be used may be selected based,for example, on a shuffle-sharding algorithm in some embodiments, suchthat packets of a particular flow from a particular endpoint aredirected to one of a subset of the AINs of the cell. Individual ones ofthe AINs may comprise or have access to a respective action cache, suchas action cache 121A. An action cache may be indexed by a combination ofattributes of the received packets, such as the combination of anidentifier of the sending client, the source and destination IPaddresses, the source and destination ports, and so on. Actions may bestored in executable form in the caches in some embodiments, e.g., usingbyte code expressed using instructions of a register-based virtualmachine optimized for implementing network processing operations. AIN120C may try to look up a representation of an action for the receivedpacket in its cache. If such an action is found, the packet may beprocessed using a “fast path” 166 in the depicted embodiment. Forexample, an executable version of the action may be implemented at AIN120C, resulting in the transmission of the contents of the packet on apath towards one or more destination endpoints, such as TE 112E inisolated network 110B. The path may include zero or more additionalAINs—e.g., as shown using arrows 161 and 162, the contents of the packetmay be transmitted via AIN 120B to TE 112E in the depicted fast packetpath. AIN 120B may have a virtual network interface configured to accessTE 112E, for example, while AIN 120C may not have such a virtual networkinterface configured, thus resulting in the transmission of the packet'scontents via AIN 120B. Note that at least in some embodiments, one ormore header values of the packet may be modified by the action (e.g., inscenarios in which overlapping private address ranges happen to be usedat the source and destination isolated networks, as discussed below infurther detail)—that is, the packet eventually received at thedestination endpoint 112E may differ in one or more header values fromthe packet submitted from the source endpoint 112K.

If an AIN's local action cache does not contain an action for a receivedpacket, a somewhat longer workflow may ensue. Thus, for example, if apacket is received from TE 112P at AIN 120M (as indicated via arrow167), and a cache miss occurs in AIN 120M's local cache when a lookup isattempted for the received packet, AIN 120M may send an action query toa selected DMN (DMN 122D) in its IPCC 127B, as indicated by arrow 168.The DMN 122D may determine, e.g., based on a client-supplied policyindicating that a multicast operation is to be performed, and based onforwarding/routing metadata provided by the client, that the contents ofthe packet are to be transmitted to a pair of endpoints 112R and 112V inisolated networks 110K and 110L respectively in the depicted example. Arepresentation of an action that accomplishes such a multicastingoperation may be sent back to AIN 120M, stored in its local cache, andexecuted at AIN 120M, resulting in the transmissions illustrated byarrows 169 and 170. In this example, AIN 120M can send outbound packetsdirectly to the destination TEs 112R and 112V, and may not need to use apath that includes other AINs of IPCC 127B.

As the traffic associated with the applications flows via the IPCCs 127,their respective ANs may collect various types of metrics. Based atleast partly on the metrics, as and when needed, additional AINs, DMNs(or even ANs) may be instantiated in various embodiments. At least insome embodiments, different IPCCs may have differing initialconfigurations—e.g., some IPCCs may start out with 10 AINs and 3 DMNs,others with 20 AINs and 7 DMNs, and so on. If the total workload beinghandled by the current set of IPCCs exceeds a threshold, new IPCCs maybe instantiated and assigned to new application instances (or, viaapplication migration, to existing application instances) in someembodiments. Similarly, if the overall workload falls below a threshold,or the resource utilization metrics of one or more IPCCs falls belowsome threshold, selected IPPCs (or individual nodes within selectedIPPCs) may be decommissioned in various embodiments. Some applicationinstances may potentially generate more traffic than can be handled bythe maximum capacity that be provisioned by a given IPCC—in suchscenarios, multiple IPCCs may be used in at least one embodiment for agiven application instance.

Interactions Among Cell Components

FIG. 2 illustrates a high-level overview of example interactions amongcomponents of an isolated cell designated for a particular applicationat a packet processing service, according to at least some embodiments.In the depicted embodiment, an isolated packet processing cell 227 of apacket processing service (PPS) similar to that discussed in the contextof FIG. 1 has been designated for a particular application. Clients 210of the PPS may submit programmatic requests 243 to the PPS control plane214 in the depicted embodiment, e.g., via a web-based console,command-line tools, APIs, graphical user interfaces or the like. Therequests 243 may indicate the types of applications to be set up (e.g.,policies to be implemented for packet processing), desired performanceor other goals to be met by the configurations set up for theapplications etc. Based on the requirements of the client and/or on theavailability and current resource consumption levels at various IPPCs,the PPS control plane 214 may designate IPPC 227 for the client in thedepicted embodiment.

Configuration metadata 205 such as forwarding information base (FIB)entries provided by the client, policies/rules indicated by the clientetc., to be used for making packet processing decisions, may betransmitted to one or more decision master nodes 225 of IPPC 227 fromthe PPS control plane 214 in the depicted embodiment. In someembodiments, the configuration metadata may be transmitted first to theIPPC administration nodes (ANs) 270, and from there to the decisionmaster nodes (DMNs) 225. In some embodiments in which a given IPPC 227comprises multiple DMNs, all the DMNs may be provided all the metadatapertaining to the one or more applications to which the IPPC isassigned. In other embodiments, respective subsets of metadata may beprovided to individual DMNs.

When a packet is received from a source traffic endpoint 264 of theapplication at an action implementation node (AIN) 268, an attempt maybe made to find a corresponding action in an action cache 297. If suchan action is found, e.g., via a lookup using a key based on somecombination of packet header values, a client identifier, and so on, theaction may be implemented, resulting in the transmission of at leastsome contents of the received packet to one or more destination trafficendpoints 272 in the depicted embodiment. This “fast path” packetprocessing pathway, in which a cache hit occurs at an AIN, and in whichdecision master nodes are not directly involved, may be much morefrequently encountered in practice in various embodiments than theslower cache miss case. Note that at least for some applications, thetotal number of packets for which the same logical action is to beimplemented may be quite large—e.g., hundreds or thousands of packetsmay be sent using the same long-lived TCP connection from one sourceendpoint to a destination endpoint.

In the scenario in which the arrival of a packet results in a cache missat the AIN 268, a request-response interaction with a DMN 225 may beinitiated by the AIN in the depicted embodiment. An action query (whichmay in some implementations include the entire received packet, and inother implementations may include a representation or portion of thepacket such as some combination of its header values) may be submittedfrom the AIN 268 to the DMN 225. The DMN 225 may, for example, examinethe contents of the action query and the configuration metadata 205, anddetermine the action that is to be implemented for thecache-miss-causing packet and related packets (e.g., packets belongingto the same flow, where a flow is defined at least partly by somecombination of packet header values) in the depicted embodiment. In atleast some embodiments, a DMN 225 may comprise an action code generator226, which produces an executable version of the action that (a) can bequickly executed at an AIN and (b) need not necessarily be interpretedor “understood” at the AIN. In at least one embodiment, the generatedaction may comprise some number of instructions of an in-kernelregister-based virtual machine instruction set which can be used toperform operations similar to those of the extended Berkeley PacketFilter (eBPF) interface. The action may be passed back to the AIN forcaching, and for implementation with respect to the cache-miss-causingpacket in at least some embodiments.

At the AIN 268 that submitted the action query, the generated action maybe stored in the cache 297, and re-used as needed for other packets inaddition to the first packet that led to the identification andgeneration of the action in various embodiments. Any of a variety ofeviction policies 298 may be used to remove entries from the caches297—e.g., if no packet requiring the implementation of a given action A1has been received for some threshold time interval, in one embodiment A1may be removed from the cache. In at least one embodiment, individualentries in the cache may have associated usage timing records, includingfor example a timestamp corresponding to the last time that action wasperformed for some packet. In such an embodiment, an entry may beremoved from the cache if/when its usage timing record indicates that aneviction criterion has been met (e.g., when the action has not beenperformed for some threshold number of seconds/minutes). In someembodiments, cached actions may periodically be re-checked with respectto the current state of the configuration metadata 205—e.g., every Tseconds (where T is a configurable parameter) the AIN may submit are-verification query indicating a cached action to the DMN layer, and aDMN may verify that the cached action has not been rendered invalid bysome newly updated configuration metadata entries. In at least oneembodiment, a DMN may send invalidation messages to the AINs when newconfiguration metadata 205 supersedes or invalidates one or more actionsthat were generated earlier. Note that in various embodiments, as longas the action that is eventually performed for a given received packetis correct, from a functional perspective it may not matter whether theaction was cached at the AINs or had to be generated at the DMNs. Assuch, even if an action is occasionally evicted from a cache 297unnecessarily or as a result of an overly pessimistic eviction decision,the overall impact on the packet processing application is likely to besmall (as long as unnecessary evictions are not very frequent) in suchembodiments. The IPPC administration nodes 270 may receive monitoring ormetric-related messages 208 from the AINs and/or the DMNs in someembodiments, and transmit administrative commands (such as restartcommands, shutdown/startup commands) and the like to the AINs and/orDMNs in at least some embodiments. In at least one embodiment, the IPPCadmin nodes 270 may initiate reconfiguration of the IPPC 227 based ongathered metrics, e.g., by adding or removing other nodes, changing VNIsettings and the like.

Cells Implemented Using Multiple Availability Containers

As mentioned earlier, in some embodiments, at least some cells of apacket processing service similar to that discussed in the context ofFIG. 1 may be implemented using resources of a provider network, such asvirtual machines implemented at a virtual computing service. FIG. 3illustrates an example scenario in which an isolated packet processingcell may comprise nodes distributed among multiple availabilitycontainers of a virtualized computing service, according to at leastsome embodiments. In the depicted embodiment, a provider network 302 maycomprise a virtualized computing service (VCS) 305 at which isolatedvirtual networks may be established on behalf of various customers orclients. An isolated virtual network or IVN (such as IVNs 310A and 310B,which may be established for one or more VCS customers, and IVN 310C,which may be configured to implement an IPCC of the packet processingservice itself) may comprise a collection of networked resourcesallocated to one client/customer of the VCS. Such resources (including,for example, virtual machines), may be logically isolated from (and bydefault, inaccessible from) resources allocated for other clients inother isolated virtual networks in at least some embodiments. In thedepicted embodiment, the packet processing service itself may beconsidered a client or customer of the VCS 305—that is, the packetprocessing service may be built by leveraging the functionalitysupported by the VCS 305. The client on whose behalf an IVN isestablished may be granted substantial flexibility regarding networkconfiguration for the resources of the IVN—e.g., private IP addressesfor virtual machines may be selected by the client without having toconsider the possibility that other resources within other IVNs may havebeen assigned the same IP addresses, subnets of the client's choice maybe established within the IVN, security rules may be set up by theclient for incoming and outgoing traffic with respect to the IVN, and soon.

In at least some embodiments, the resources of the VCS 305, such as thehosts on which various virtual machines are run, may be distributedamong a plurality of availability containers 350, such as 350A and 350B.As mentioned earlier, an availability container in turn may compriseportions or all of one or more distinct locations or data centers,engineered in such a way (e.g., with independent infrastructurecomponents such as power-related equipment, cooling equipment, orphysical security components) that the resources in a given availabilitycontainer are insulated from failures in other availability containers.A failure in one availability container may not be expected to result ina failure in any other availability container; thus, the availabilityprofile of a given resource is intended to be independent of theavailability profile of resources in a different availability container.

In the depicted embodiment, action implementation nodes (AINs) 325,decision master nodes (DMNs) 327, and administration nodes (ANs) 329 mayall be implemented at least in part using respective virtual machines(VMs) 320 of the VCS 305. As shown, AINs 325A, 325B, 325C, 325D, 325Eand 325F may be implemented at virtual machines 320A, 320B, 320C, 320F,320G and 320H respectively. DMNs 327A, 327B, 327C and 327D may beimplemented at virtual machines 320D, 320E, 320J and 320K respectively,and ANs 329A, 329B, 329C and 329D may be implemented at VMs 320L, 320M,320N and 320P respectively. In some embodiments, a given VM 320 may beinstantiated at a respective physical virtualization host; in otherembodiments, multiple VMs may be set up at a given physical host. Theillustrated cell, implemented in IVN 310C, may comprise at least twodata-plane subnets 340A and 340B, and at least two control-plane subnets342A and 342B. One data plane subnet and one control plane subnet may beimplemented in each of at least two availability containers 350—e.g.,subnets 340A and 342A may be configured in availability container 350A,while subnets 340B and 342B may be configured in availability container350B. A control-plane subnet 342 may comprise one or more ANs 329 atrespective VMs 320 in some embodiments, while a data-plane subnet 340may comprise one or more AINs 325 and one or more DMNs 327 at respectiveVMs 320. As a result of the use of multiple availability containers, theprobability that the entire IPPC is affected by any given failure eventmay be minimized in the depicted embodiment. The use of differentsubnets for control-plane versus data-plane nodes may help to separateat least the majority of the control plane traffic of the IPPC from thedata plane traffic of the IPPC in various embodiments.

As shown, the IPPC implemented using IVN 310C may be used for packetprocessing applications involving traffic between at least four isolatednetworks—IVNs 310A and 310B, and customer-premises isolated networks390A and 390B in the depicted embodiment. IVNs 310A and 310B may eachcomprise, for example, a set of virtual machines 310 (e.g., 310A, 310B,310C or 310D) set up on behalf of a VCS customer. Isolated network 390A,which may for example be set up at a customer premise or locationoutside the provider network's own data centers and may include somenumber of hosts such as host 395A, may communicate with the IPPC via aset of virtual private network (VPN) pathways 308 in the depictedembodiment. Isolated network 390B may also be set up at a set ofcustomer premises or locations outside the provider network 302 and maycomprise some number of hosts such as host 395K in the depictedembodiment. Traffic between the isolated network 390B and the IPPC mayflow over a set of dedicated physical links 309 in the depictedembodiment (e.g., instead of a set of links that may be shared withtraffic of the public Internet), which may also be referred to as“direct-connect” links. As such, the packet processing serviceimplemented using the VCS 305 of provider network 302 may be capable ofprocessing packets generated at (or directed towards) a variety ofnetwork configurations in the depicted embodiment, including (but notnecessarily limited to) isolated virtual networks within the VCS itself,external networks such as 390A which use VPN connections over sharedlinks to communicate with the VCS, and external networks such as 390Bwhich use dedicated links to communicate with the VCS. Other types ofnetworks may also be connected using the packet processing service invarious embodiments. In at least some embodiments, the nodes of theIPPCs may not utilize the type of multi-availability-containerarchitecture shown in FIG. 3, may use non-virtualized hosts instead ofor in addition to virtual machines, and/or may not necessarily use avirtualized computing service or other services of a provider network.

Multiplexed Virtual Network Interfaces

In some embodiments, a virtualized computing service (VCS) may implementvirtual network interfaces (VNIs) to help simplify various aspects ofnetworking configuration for virtual machines. As indicated earlier, avirtual network interface may comprise a set of networking configurationproperties or attributes (such as IP addresses, subnet settings,security settings, and the like) that can be dynamically associated(“attached” to) or disassociated (“detached” from) with individualvirtual machines, without for example having to make changes at physicalnetwork interfaces if and when virtual machines migrate from onephysical host to another. In some embodiments, at least one IP address“IPaddr1” may be assigned to a given virtual network interface VNI1, andsecurity rules restricting inbound and outbound traffic may be set forVNI1. When that VNI is programmatically attached to a given virtualmachine VM1 launched at a host with a physical network interface cardNIC1, network packets indicating IPaddr1 as their destination address(and complying with the security rules) may be received at VM1 via NIC1.In addition, outbound packets generated at VM1 may indicate IPaddr1 astheir source address and may be physically transmitted towards theirdestinations via NIC1. If VNI1 is then programmatically detached fromVM1 and attached to VM2 (which is executing at a different host with adifferent physical network interface card NIC2), the IPaddr1 trafficthat was previously being received at VM1 may now be received at VM2,with the same security rules in place.

Support for virtual network interfaces may considerably simplify severaltypes of network configuration tasks, including the operation of variousnodes of the packet processing service in some embodiments. When a newVNI is created, e.g., in response to a programmatic request from aclient of a virtual computing service which supports VNIs, a newinterface identifier (VNI-ID) may be generated for it. The providernetwork in which the VNI is to be used may comprise a plurality oflogical partitions (such as the isolated virtual networks (IVNs)described earlier) in some embodiments, and the attributes of the VNImay contain a logical partition identifier in such cases. In some casesthe attributes may include a zone identifier, which may for exampleindicate an availability container, a geographical region, or a set ofdata centers whose virtual machines may be available for programmaticattachment to the VNI.

Any of several types of network addressing-related fields may beincluded within the set of attributes of a VNI in different embodiments.One or more private IP addresses may be specified in some embodiments,for example. Such private IP addresses may for example be usedinternally for routing within IVNs, and may not be directly accessiblefrom outside the IVN. In general, zero or more public IP addresses mayalso or instead be associated with a given VNI in some embodiments;these IP addresses may be visible outside the provider network, e.g., tovarious routers of the public Internet or peer networks of the providernetwork. One or more subnet identifiers (e.g., expressed in ClasslessInter-Domain Routing or CIDR format) may be included within a VNI'sattributes in some embodiments, such as identifiers of subnets set up bya client within an IVN in which the VNI is to be used. In one embodimentan identification of at least one Domain Name Service (DNS) serverresponsible for propagating address(es) associated with the VNI, orother DNS-related information, may be included in VNI attributes aswell. In some embodiments VNI attributes may include security-relatedproperties. Some provider networks may allow users to specify rules,including for example firewall-related rules, for the types of incomingand/or outgoing traffic allowed at VMs to which a VNI may be attached.Such rules may be termed “security groups” and identified among a VNI'sattributes in some embodiments. Various port and protocol restrictionsmay be enforced using such rules, and multiple rules may be associatedwith each VNI. For example, a client may use security groups to ensurethat only HTTP and HTTPs outgoing or incoming traffic is allowed, tolimit the set of TCP or UDP ports to which traffic is permitted, tofilter incoming and outgoing traffic according to various policies, andso on. VNI security settings may be used to enforce cell isolationpolicies (e.g., to permit intra-IPCC traffic, and prohibit inter-IPCCtraffic) in some embodiments. A number of other attributes may also bespecified for VNIs in various embodiments, such as authorization relatedsettings/permissions and the like.

In at least one embodiment, VNIs may be arranged in a multiplexedconfiguration, making it easier to balance traffic workloads among agiven set of sources and destinations. FIG. 4 illustrates an example useof multiplexed virtual network interfaces for communications betweenisolated networks and a packet processing service, according to at leastsome embodiments. Network packets are to flow between virtual machines(VMs) 410 of at two isolated virtual networks (IVNs) 408A and 408B usingthe resources of an IPPC 450 of a packet processing service implementedat a VCS 405 in the depicted example scenario. The packet processingservice may have capabilities and features similar to the service 102discussed in the context of FIG. 1. IVN 408A includes VMs 410A and 410B,each of which may have one or more virtual network interfaces attachedin the depicted embodiment; similarly, IVN 408B comprises at least VMs410C and 410D. In addition, the IVNs 408A and 408B may also each includea client-side VNI (CVNI) 412 set up to handle traffic directed to orreceived from other IVNs via the packet processing service in thedepicted embodiment. Thus, IVN 408A comprises CVNI 412A, while IVN 408Bcomprises CVNI 412B. In various embodiments, APIs or other programmaticinterfaces implemented by the packet processing service may be used toassociate VNIs to be used for receiving/transmitting packets fromisolated virtual networks 408A with AINs. For example, in response toobtaining an indication of a particular VNI (e.g., a CVNI 412) to beused for transmitting an application's packets to one or more actionimplementation nodes (AINs) of an IPPC, metadata indicating anassociation between the application, the VNI, and the IPPC may be storedat a control plane repository of the packet processing service in atleast some embodiments. Similarly, metadata pertaining to the IPPC 450,assigned to process packets flowing between IVNs 408A and 408B, maycomprise a set of data plane nodes implemented at respective virtualmachines in the depicted embodiment, such as action implementation nodes(AINs) 425A-425D at VMs 420A-420D, and decision manager nodes (DMNs)427A and 427B at VMs 420K and 420L. An intermediary VNI multiplexingresource pool 415, comprising at least some number of client-facingservice endpoint addresses (CSEAs) 422 and some number of trunk VNIs 432may be utilized for communications between the AINs 425 and the IVNs 408in at least some embodiments.

In at least some embodiments, a client-facing service endpoint addressor CSEA 422 (which may, for example, be provided to a client in responseto a request to attach an IVN to an instance of a packet processingapplication, such as a virtual traffic hub) may in effect serve as anidentifier or target address of the packet processing service from theperspective of the IVN for which the CSEA is configured. Thus, in someembodiments the virtualization management stack (e.g., a hypervisor oran offloaded virtualization manager component) that transmits a networkpacket originating at a VM 410 of an IVN 408 may use the CSEA as adestination of an encapsulation packet, instead of having to obtainaddresses of individual AINs. Individual AINs 425 may have their owntrunk VNIs (TVNIs) 432 configured to receive packets that wereoriginally directed to any of several CSEAs 422—e.g., each on the TVNIs432 may receive packets directed to CSEA 422A (from IVN 408A) or 422B(from IVN 408B) in the depicted example scenario. A given CSEA may beused to direct packets to any of several AINs (e.g., using a shufflesharding algorithm to select the particular AIN for a given packet),representing one level of multiplexing in the depicted embodiment. In asecond level of multiplexing, a given TVNI 432 (e.g., TVNI 432A attachedto VM 420A at which AIN 425A is instantiated, TVNI 432B attached to VM420B of AIN 425B, TVNI 432C attached to VM 420C of AIN 420C, or TVNI432D attached to VM 420D of AIN 425D) may receive packets from (ortransmit packets to) VMs any of several IVNs in the depicted embodimentvia the respective CSEAs 422 of the IVNs. Using this multiplexingapproach in combination with the IPPCs of the packet processing service,numerous (e.g., tens or hundreds of thousands of) resources at a largenumber of isolated networks may be able to communicate with one anotheraccording to client-selected policies and client-provided metadata invarious embodiments. In at least some embodiments, a given TVNI mayitself be programmatically associated with multiple branch VNIs, e.g.,with respective distinct IP addresses and security settings, enablingeven more sophisticated multiplexed traffic management at individual VMs420. It is noted that in at least some embodiments, multiplexingtechniques such as those shown in FIG. 4 may not be employed.

Packet Flow Identifier Elements

In at least some embodiments, a given action, generated based on aclient-selected policy at the decisions layer of a packet processingservice (PPS) similar to service 102 of FIG. 1, may potentially beapplied to a group of related packets referred to as a packet flow, orsimply as a flow. FIG. 5 illustrates example packet flow identifierelements and example packet processing policy elements, according to atleast some embodiments. A flow may be characterized (or distinguishedfrom other flows) based on one or all of the following attributes orelements 520 of packets received at the packet processing service in thedepicted embodiment: the network protocol 521 used for sending thepacket to the PPS, the source network address 522, the source port 523,the destination network address 524, the destination port 525, and/or anapplication identifier 526 (e.g., an identifier of a specific virtualnetwork interface set up for communications between an isolated networkand the PPS). In some embodiments the direction in which the packets aretransmitted (e.g., towards the PPS, or away from the PPS) may also beincluded as an identifying element for the flow. A number of differentnetworking protocols may be supported in different embodiments—e.g.,including the Internet Protocol (IP), the Transmission Control Protocol(TCP), the User Datagram Protocol (UDP), the Internet Control MessageProtocol (ICMP), protocols that do not belong to or rely on the TCP/IPsuite of protocols, and the like. The particular combination ofattributes that are used to distinguish one group of packets fromanother for a given packet processing application requirement or clientmay be referred to collectively as packet flow identifier elements 520in some embodiments. The process of selecting a particular node or cellfrom among the accessible nodes/cells of the action implementation layermay include flow hashing (e.g., in addition to or instead of shufflesharding) in some embodiments. Some or all of the packet flow identifierelements 520 of a given packet may be aggregated (e.g., viaconcatenation or using some other function) in some implementations, andthe result of the aggregation may be provided as input to a selectedhash function, with the output of the hash function used to select theparticular node or cell as part of the flow hashing.

As mentioned earlier, in various embodiments clients of the packetprocessing service may indicate policies that are used at the decisionmasters to generate actions for various flows. A given policy may inturn include several types of rules, parameters or elements 540 in thedepicted embodiment. The particular set of parameters used for a givenclient's application may differ from the set of parameters used for adifferent application of the same client (or from the parameter set usedfor some other client's application). A payload replication rule 541 mayindicate how many replicas of a given received packet's contents or bodyare to be transmitted to respective destinations—e.g., if a multicastprotocol is to be implemented for a given client and the destinationmulticast group contains eight endpoints, the payload replicationparameter may indicate that eight replicas are to be transmitted. Bydefault, e.g., if a payload replication rule is not included, a singleoutbound or transformed packet may be generated corresponding to eachreceived packet in some embodiments.

For some packet processing applications, in some embodiments the PPS mayact as a protocol translator—e.g., incoming packets may be received viaa particular networking protocol (such as TCP), while correspondingoutgoing packets may be sent via a different protocol (such as UDP, or acustom networking protocol that is not part of the TCP/IP family ofprotocols). The protocol for sent packets element 542 of the policy mayindicate whether such a protocol change is to be implemented, and if so,the specific protocol to be used for the transformed packets. Sourcesubstitution rule 543 may indicate whether the source address and/orsource port are to be changed, and if so, the acceptable source(address, port) range to be used for the transformed packets in variousembodiments. Similarly, destination selection rule 544 may indicatewhether the destination address and/or port is to be changed as part ofa packet transformation, and if so, what the acceptable destinationaddresses and/or ports are for the flow being considered. In some cases(e.g., for multicast), multiple destinations may be indicatedcorresponding to a given received packet. In some embodiments, at leastsome packet processing policies may not take all the different elements540 shown in FIG. 5 into account, and/or parameters not shown in FIG. 5may be considered for some packet processing policies.

Example Application Categories

FIG. 6 illustrates example categories of packet processing applicationsthat may be implemented using a cell-based packet processing service,according to at least some embodiments. As shown, application categories600 in the depicted embodiment may include, for example, scalablecross-IVN (isolated virtual network) channels 606, scalable VPN (virtualprivate network) connectivity 608, scalable dedicated-link connectivity610, multicast 612, address substitution 616, and the like. Other typesof packet processing applications may be supported in variousembodiments. In general, a packet processing service with capabilitiessimilar to that of the service shown in FIG. 1 may be configurable toimplement any desired type of packet processing or transformations (orcombinations of different types of packet processing ortransformations), with nodes being assignable dynamically at each layerto support a large range of traffic rates in a transparent and scalablemanner.

In some embodiments, as described earlier, the packet processing servicemay be implemented at a provider network in which isolated virtualnetworks can be established. In such embodiments, the packet processingservice may be used for an application, such as a virtual traffic hub,that acts as intermediary or channel between the private address spacesof two or more different IVNs, in effect setting up scalable and securecross-IVN channels 606. In at least some embodiments, the PPS may alsoor instead be used to support scalable VPN connectivity 608 between someset of resources within a provider network and one or more clientnetworks or client premises outside the provider network, or betweenmultiple client-premises networks each linked via VPN connections to thePPS. In some embodiments, a provider network may support connectivity610 with external networks via dedicated physical links called “directconnect” links, and the traffic between such external networks (andbetween such external networks and IVNs or VPN-connected externalnetworks) may be managed using the packet processing service. Addresssubstitution 616, as the name suggests, may involve replacing, for thepackets of a particular flow, the source address and port in aconsistent manner. Such address substitution techniques may be useful,for example, when an overlap exists between the private address rangesof two or more isolated networks, and the packet processing service maybe employed as the intermediary responsible for such substitutions insome embodiments. Multicast 612 is a networking technique, implementableusing a PPS in some embodiments, in which contents (e.g., the body) of asingle packet sent from a source are replicated to multiple destinationsof a specified multicast group. Note that at least in some embodiments,a single instance of an application may combine several of the packetprocessing functions indicated in FIG. 6 (and/or other packet processingtechniques). For example, a single instance of a virtual traffic hubapplication (of the kind discussed below in further detail) built usingthe PPS may concurrently implement scalable cross-IVN channels, scalableVPN connectivity, scalable dedicated-link based connectivity, and so onin some embodiments. Other categories of packet processing applicationsmay be supported using the PPS in different embodiments, while at leastsome of the types of applications indicated in FIG. 6 may not besupported in some embodiments.

Cell Configuration Parameters

As discussed earlier, in various embodiments a packet processing servicesimilar to that shown in FIG. 1 may be organized as a collectionisolated cells, enabling the resources assigned to differentapplications to be managed separately. FIG. 7 illustrates exampleconfiguration parameters of a cell of a packet processing service,according to at least some embodiments. At least some of theseparameters may be set based on input provided by clients on whose behalfpacket processing applications are to run in various embodiments. Thepacket processing service may assign default values to one or more ofthe parameters in at least one embodiment.

Initially, when a new isolated packet processing cell (IPPC) is set up,it may be provisioned with a default or baseline number of actionimplementation nodes (AINs), decision master nodes (DMNs) andadministration nodes (ANs) in the depicted embodiment. The control planecomponents of the packet processing service may analyze variouscollected metrics, such as resource utilization levels, responsiveness,and the like, of the data plane nodes including the AINs and the DMNs,as well as ANs themselves in various embodiments, and increase/decreasethe number of nodes at the various layers as needed based on thresholdconditions being met. IPPC parameters 700 may include the initial,minimum and maximum number of AINs 704, DMNs 706 and ANs 708 in thedepicted embodiment. In some embodiments, the ratio of the number ofnodes at different layers may be kept fixed (e.g., for every DMN, twoAINs may be configured), so that when the number of nodes at a givenlayer is modified, that change is accompanied by proportional changes atother layers.

As mentioned earlier, in at least some embodiments, AINs, DMNs and/orANs may be implemented as programs running on virtual machines, and agiven virtualization host may be able to support multiple virtualmachines. Even in scenarios in which virtual machines are not used,e.g., when the individual nodes at one or more layers comprise one ormore processes running within operating systems on un-virtualizedphysical machines, in some implementations multiple nodes of one or morelayers may be instantiated at a given host. The node-to-host mappingsparameter 710 may indicate how many nodes at the various layers are tobe implemented at a given host in the depicted embodiment.

A tenancy settings parameter 712 may govern whether the cell is to beused for a single application of a single client, multiple applicationsof only a single client, or multiple applications of respective clientsin some embodiments. Availability settings 714 may indicate, forexample, the minimum/default/maximum number of availability containersto be used for the nodes of the IPPC in some embodiments. Shufflesharding parameters 716 may indicate how many different AINs of the IPPCare to be used for packets associated with a given source or destinationendpoints, and how much overlap is permitted between the sets of AINsused for different endpoints in the depicted parameter. According to ashuffle sharding algorithm, if the IPPC comprises N AINs, packets from agiven source endpoint E1 may be directed (e.g., based on hashing ofpacket header values) to one of a subset S1 of K AINs (K<N), and packetsfrom another source endpoint E2 may be directed to another subset S2 ofK AINs, where the maximum overlap among S1 and S2 is limited to L commonAINs. Migration triggering parameters 718 may indicate the thresholdconditions which are to result in the initiation of an applicationmigration from one IPPC to another (an example of a multi-phasemigration procedure is provided below). Scale-up/down triggeringparameters 720 may indicate under what conditions new AINs, DMNs and/orANs are to be instantiated within the IPPC, and under what conditionsthe number of AINs, DMNs and/or ANs is to be reduced. In someembodiments, the management of an IPPC may be guided by parametersettings other than those shown in FIG. 7. In at least one embodiments,one or more of the parameters 700 may not be used.

Application Migration Across Cells

As suggested above, one of the tenets of the cell-based design of thepacket processing service of the kind introduced above is to minimizeinteractions across cell boundaries. When a multi-tenant mode ofoperation is being used, however, it may sometimes be the case that thetotal workload of the set of applications to which a given IPPC isassigned becomes too large to be handled by the maximum number of AINs,DMNs and ANs that the cell can accommodate. In such scenarios, thetraffic associated with a given application may be migrated to adifferent IPPC in at least some embodiments. Such migrations may also beinitiated in some embodiments even if the source IPPC (the IPPC fromwhich the application is being migrated) is operating in single-tenantmode—e.g., when the application's workload exceeds the maximum capacityof the source IPPC, a larger IPPC may have to be employed.

FIG. 8, FIG. 9, FIG. 10 and FIG. 11 collectively illustrate an exampletechnique for migrating traffic of an application between cells of apacket processing service, according to at least some embodiments. FIG.8 illustrates the pre-migration scenario 802. An IPPC 850A (the sourceIPPC from which application is to be migrated) is being used to provideconnectivity between two isolated virtual networks (IVNs) 810A and 810Bof a virtualized computing service. IPPC 850A comprises AINs 825A-825Drunning on virtual machines (VMs) 820A-820D, as well as DMNs 827A and827B running on VMs 820K and 820L. Cell metadata 829A of IPPC 850A maycomprise, for example, forwarding information base entries,configuration settings identifying the set of AINs and DMNs being used,health information of the DMNs and AINs etc. A virtual network interface(VNI) multiplexing resource pool is being used for connecting the IVNsto the AINs in the depicted embodiment, using techniques similar tothose shown in FIG. 4. For IVN 850A, which has a client-side virtualnetwork interface 812A and a collection of VMs such as 810A and 810Bfrom which packets directed to IVN 850B originate (and at which packetsoriginating at IVN 850B may be received), a client-facing serviceendpoint address (CSEA) 822A has been configured. Individual ones of theAINs 825A-825D have an attached trunk VNI 832 (TVNIs 832A-832D), andtraffic being received at CSEA 822A is being distributed among a groupof 3 TVNs—TVN 832A 832B and 832C e.g., in accordance with a shufflesharding algorithm in the depicted embodiment. Similarly, CSEA 822B isestablished for traffic associated with the CVNI 812B and VMs 810C and810D of IVN 850B in the depicted example scenario. IPPC 850B, which hasits own set of DMNs and AINs running on VMs with attached TVNIs, is notcurrently in use for the traffic flowing between IVNs 850A and 850B.

In various embodiments in which multiple paths between a CSE 822 and theTVNIs 832 may potentially be available, respective path selectionweights (PWs) may be used to control which paths are actually to beused; for example, a PW value of 1 may indicate that the path is to beused for at least some time interval, while a PW value of 0 may indicatethat the path is not to be used for at least some time interval. Asshown, in the pre-migration scenario 802, path selection weights “1”have been assigned to three paths each between CSEAs 822 and the TVNIsof IPPC 850A. Traffic is flowing between the VMs of IVNs 850A and 850B,via the IPPC 850A, in accordance with a policy and forwarding metadataspecified by a client.

At some point, a decision to migrate the application to IPPC 850B may bemade (e.g., based on analysis of metrics obtained from IPPC 850A and/orIPPC 850B), and a phased migration technique may be initiated in thedepicted embodiment. The first stage or phase of the migration isillustrated in FIG. 9. As shown, in this stage, configuration changes(e.g., programmatic associations of CSEAs with TVNIs) may be performedto enable traffic to flow between the CSEAs 822 and the TVNs of the IPPC850B, with three TVNs out of the four (TVNIs 832E-832H) being selectedfor each CSEA 822 (the same number of TVNIs as were being used at IPPC850A in the pre-migration scenario). In addition, at least a portion ofthe cell metadata 828A may be copied to IPPC 870, as indicated by arrow870. At this first stage, however, path selection weights of zero may beassigned for a brief period to the new paths (e.g., between CSEA 822Aand TVCNs 832E-832G, and between CSEA 822B and TVNIs 832F-832H), so theapplication traffic continues to be processed at IPPC 850A. The briefassignment of zero weights may, for example, enable configurationinformation to be propagated to the destination cell AINs (AINs825E-825H) before the implementation of the application's actions isinitiated at the destination IPPC 850B.

Stage 2 of the migration procedure is illustrated in FIG. 10. At thisstage, the path selection weights for both sets of paths may briefly beset to 1, enabling traffic to be directed to both the source anddestination IPPCs. As discussed earlier, flow hashing may be used toselect individual AINs (from either IPPC) for individual packet flows.Because both cells contain the metadata needed at the DMNs to generatethe actions to be implemented, and all possible intra-IPPC (AIN-to-AIN)forwarding paths exist at both IPPCs, all received packets may beprocessed and forwarded correctly in Stage 2, without requiring packetsto be transmitted between the IPPCs 850A and 850B. Metadata changes, ifany are indicated by the client, may be propagated to both IPPCs asindicated by arrow 872, keeping both sets of metadata effectively insync in the depicted embodiment. Note that the replication andpropagation of cell metadata, indicated by arrows 870 and 872 in FIG. 9and FIG. 10 respectively, represent control-plane operations and may beaccomplished without using data plane resources in at least someembodiments.

In the final stage (Stage 3) of the migration, depicted in FIG. 11, thepath selection weights assigned to the paths that were being usedpre-migration may be set to zero, thereby draining the traffic from IPPC850A and directing all the traffic between IVNs 810A and 810B to IPPC850B. The portion of cell metadata 828A corresponding to the migratedapplication may be deleted from IPPC 850A as indicated by arrow 874 inthe depicted embodiment. Using the multi-stage approach illustrated inFIG. 8-FIG. 11, applications may be transferred from one IPPC to anotherwithout requiring data plane packets to be transferred across cellboundaries in various embodiments, thereby complying with the cell-basedisolation principle underlying the design of the packet processingservice.

Control Plane Overview

FIG. 12 illustrates example control-plane elements of a packetprocessing service, according to at least some embodiments. As shown, anAPI handler fleet 1290 of a packet processing service with features andcapabilities similar to that of service 102 of FIG. 1 may be establishedto receive programmatic requests from clients 1292 in the depictedembodiment. In some embodiments, API handlers of fleet 1290 may beresponsible for assigning a particular isolated packet processing cell(IPPC) 1210, such as IPPC 1210A or 1210B, for a given client'sapplication instance. In other embodiments, a separate cell mappingmanager fleet may be responsible for the assignment of IPPCs to clients.

Control plane or administrative information may be managed using anumber of components within a given IPPC, as well as a collection ofnetwork-accessible services other than the packet processing serviceitself in the depicted embodiment. As shown, a given IPPC such as 1210Aor 1210B may comprise at least one administration node (AN) 1250 such as1250A or 1250B. An AN 1250 may in turn comprise a cell-levelcontrol-plane API manager 1274 (e.g., 1274A or 1274B), a cell-levelhealth manager 1262 (e.g., 1262A or 1262B), and/or a cell-level metricsaggregator 1260 (e.g., 1260A or 1260B). The cell-level API manager 1274may, for example, receive administrative commands from, and provideresponses to, the API handler fleet 1290. Such administrative commandsmay, for example include startup/shutdown commands to be transmitted tovarious data plane nodes and/or other configuration change requests.Configuration information 1272 (e.g., 1272A or 1272B) of the IPPC (e.g.,the number and identifiers of the data plane nodes, shuffle-shardingparameters, and the like) may be stored at a separate repository in someembodiments, such as a high-performance key-value database service. Inat least one embodiment, a network-accessible data stream managementservice may be used to store various metrics streams 1252 (e.g., 1252Aor 1252B) collected from the data plane and control plane nodes of theIPPC, such as resource usage and other performance measurements, thenumber of packet processing actions performed per flow or perapplication during various intervals, and so on. In the depictedembodiment, a cell-level health manager 1262 may be responsible forcollecting node health information pertaining to various nodes of theIPPC and providing the health information to higher-level health dataaggregators.

While the decision master nodes (DMNs) may primarily perform data planefunctions in various embodiments, they may need to obtain metadata(e.g., forwarding information base contents and the like) provided tocontrol plane components by service clients. Accordingly, in at leastsome embodiments, one or more of the DMNS 1225 (e.g., DMN 1225A or1225A) may comprise a respective metadata reader 1228 (e.g., 1228A or1228B) that obtains client-supplied metadata 1230 (e.g., 1230A or 1230B)needed for determining and generating packet processing actions. In someembodiments, when such metadata is received at the API handler fleet1292, it may be stored as one or more objects within an object storageservice, and the metadata readers 1228 of the DMNs of the IPPC for whichthe metadata may be provided the identifiers of the objects and theappropriate credentials to access the objects. In some embodiments, apush methodology may be used to propagate the metadata—e.g., whenever aclient supplies a new version or update, that new version may beimmediately transmitted to the metadata readers. In other embodiments, apull methodology may be employed, in which the metadata readersperiodically check for updated client metadata, or a combination of apull and push methodology may be employed in which the metadata readersperiodically verify that they have the most recent metadata.

In various embodiments, cell level metadata and metrics may be collectedfrom a plurality of IPPCs 1210 of the packet processing service andstored in an aggregate metadata/metrics store 1272 (which may, forexample, also comprise some number of tables in a high performancekey-value database). Such aggregated information may be used, forexample, to enable the operator of the packet processing service toanalyze trends across different applications and clients, make long-termequipment acquisition plans and the like.

Node Health Management

A packet processing service may be responsible for ensuring thatsufficient numbers of nodes of the data plane remain operational andresponsive in order to be able to process the workloads of clientapplications. In order to do so, multiple availability containers of thekind introduced above, as well as a number of node health monitoring andanalysis techniques may be implemented in various embodiments. FIG. 13illustrates example pathways of health-related messages among nodes ofan isolated packet processing cell, according to at least someembodiments. In the depicted embodiment, an isolated packet processingcell 1350 of a packet processing service similar to that discussedearlier comprises AINs 1325 and DMNs 1327 distributed among twoavailability containers 1340A and 1340B of a provider network. DMN1327A, as well as AINs 1325A, 1325B and 1325C are instantiated inavailability container 1340A, while DMN 1327B, AINs 1325D, 1325E and1325F are instantiated in availability container 1340B.

In the depicted embodiment, individual ones of the AINs 1325 may beresponsible for monitoring and communicating health (e.g., nodereachability and responsiveness) information pertaining to other AINsand/or DMNs of the cell. As such, a given AIN 1325 may send health probemessages periodically to each other AIN of the IPPC, including AINs inits own availability container as well as other availability containersbeing used by the IPPC, and receive corresponding responses from each ofthe other AINs. For example, as shown, AIN 1325A may send probes notjust to AINs 1325B and 1325C in its own availability container 1340A,but also to AINs 1325D-1325F in availability container 1340B.Furthermore, a given AIN 1325A may also be configured to send healthprobes to DMNs 1327 within its own availability container 1340—e.g.,each of AINs 1325A, 1325B and 1325C of availability container 1340Asends health probes to DMN 1327A within the same availability container1340A, while in availability container 1340B each of AINs 1325D, 1325Eand 1325F sends health probes to DMN 1327B. In at least someembodiments, a form of piggybacking may be used for at least some healthinformation messages 1302. For example, when sending a health probemessage to a DMN 1327, an AIN may include the latest health information(e.g., reachability status or the like) available at the AIN regardingother nodes in the message. In at least one embodiment, when a DMN 1327replies to a health probe, it may include a timestamp indicating whenits local metadata reader obtained the most recent version of theclient-supplied metadata used to make packet processing decisions at theDMN. In some embodiments, the health information collected at AINs/DMNsof individual availability containers being used for one or more cellsmay be stored at aggregated tables, such as per-availability-containertables 1355A and 1355B.

A given AIN or DMN may itself comprise a plurality of execution engines,such as respective virtual cores or threads in embodiments in whichvirtual machines are being employed for IPCC nodes. FIG. 14 illustratesan example technique which may be employed to gather health informationwithin an action implementation node of a packet processing service,according to at least some embodiments. In some embodiments, an AINexecution device/platform 1430 (e.g., a virtual machine or a physicalmachine) may comprise one or more action implementer process(es) 1440 aswell as a health agent process 1452. In some embodiments, the Data PlaneDevelopment Kit (DPDK), which comprises a set of data plane librariesand network interface controller drivers for fast packet processing, maybe used to create the programs which are manifested as the processes1440. In other embodiments, DPDK may not necessarily be used.

An action implementer process 1440 may in turn comprise an I/O manager1427 as well as some number of workers 1425, such as 1425A-1425C in thedepicted embodiment. Individual workers may be responsible forimplementing actions for a respective set of packet flows, with workersbeing selected for various flows using flow hashing in at least someembodiments. The I/O manager 1427 and/or the workers 1425 may each beimplemented using a respective virtual core or execution thread in someembodiments. The health agent process 1452 may receive health probessent from other AINs, and pass them on to the I/O manager 1427 in atleast some embodiments. The I/O manager 1427 may in turn forwardrespective health probes to each of the workers 1425, and collect thecorresponding responses. In some embodiments, the probes may beconsidered the logical equivalents of ping or heartbeat messages, andprobe responses may indicate that the probed worker is alive andresponsive as of a particular timestamp. From the individualworker-level health responses, the health status of the AIN as a wholemay be determined—e.g., in some embodiments, all the workers 1425 may beexpected to be responsive in order to declare the AIN healthy. Inaddition, the health agent process may also send health probes to otherAINs and DMNs, receive responses from those nodes (based on a similarper-worker response obtained at those nodes), and pass them on to theI/O manager in various embodiments. In at least some embodiments,individual DMNs may also comprise a health agent process and a decisionmaking process with workers and an I/O manager, and a similar healthrelated message flow to that illustrated in FIG. 14 may be employed atDMNs.

The health agent process 1452 may transmit the collected health statusfrom the action implementer process 1440 to a health information tables1455 in the depicted embodiment. The table 1455 may comprise a set 1473of cell reachability vectors (CRVs) 1472 in some embodiments. A givenCRV 1472 may, for example, include a database update timestamp 1430indicating the time at which the CRV was created/inserted into thetable, and a respective last-successful-ping-time value for individualones of the AINs (e.g., ping-time value entries 1431A-1431K) and DMNs(e.g., ping-time value entries 1432A 1432J) of the IPPC. The cellreachability vectors 1472 may be analyzed and used, for example, at thepacket processing service control plane to make decisions regardingreplacement of unhealthy nodes and the like. In the depicted embodiment,each AIN (e.g., the action implementer process of the AIN) may receiveresponses to the health probes sent from the AIN to other nodes, andconstruct a local reachability vector with entries indicating theresponsiveness of other nodes in at least some embodiments, similar inconcept to the cell reachability vectors. Similar local reachabilityvectors may also be constructed at DMNs in such embodiments. Inscenarios in which the IPPC comprises several DMNs, the localreachability information at AINs may be used to pick the “healthiest”(most responsive) DMN as the target for action queries in someembodiments. Similarly, when responding to an action request, localreachability information (which may have been provided by AINs to theDMN) may be used at a DMN to pick the healthiest (most responsive) AINfor an action in at least some embodiments, e.g., if several AINs areavailable as potential next-hops for a routing/forwarding action.

Methods for Implementing Cell-Based Packet Processing Service

FIG. 15 is a flow diagram illustrating aspects of operations that may beperformed to implement a multi-layer cell-based packet processingservice, according to at least some embodiments. As shown in element1501, a pool of isolated packet processing cells (IPPCs) of a Layer-3packet processing service (PPS), similar in features and functionalityto the PPS 102 of FIG. 1, may be established in the depicted embodiment.A given IPPC may include a selected number of AINs (actionimplementation nodes), decision manager nodes (DMNs) and administrativenodes (ANs), some or all of which may be implemented using virtualmachines of a virtualized computing service in one embodiment. Invarious embodiments, during normal operation, transmissions of packetsof at least some types (e.g., data plane packets) across cell boundariesmay generally be prohibited, but a given cell (and individual resourceswithin the cells) may be assigned to multiple applications in at leastsome embodiments. In at least one embodiment, a pool of IPPCs may be setup in advance of requests to establish particular application instances(such as virtual traffic hubs of the kind discussed below), withindividual ones of the pre-provisioned IPPCs being assigned from thepool for new application instances as needed. In other embodiments, atleast some new IPPCs may be established on demand, e.g., instead ofbeing selected from a pre-created pool.

A particular IPPC C1 may be assigned to a first application App1 with aset of source and destination endpoints in the depicted embodiment(element 1504). Such an assignment may be triggered in response to oneor more programmatic requests (e.g., a create-application-instancerequest followed by an attach-to-application-instance request, asdiscussed in further detail below) in some embodiments. In at least oneembodiment virtual network interfaces may be used for connectivitybetween AINs of C1 and the source and destination endpoints, e.g., usinga multiplexing scheme similar to that discussed earlier.

Application-specific metadata (such as entries of a forwardinginformation base) and/or a client-specified policy to be used to makepacket processing decisions may be obtained, e.g., via control-planeprogrammatic interfaces of the PPS in some embodiments (element 1507).The metadata and policy may be propagated to the DMNs of C1 in variousembodiments. In some embodiments, as discussed earlier, a fleet of APIhandlers of the PPS may receive the metadata and policies and transmitthem to one or more ANs of the relevant IPPCs, where the ANs maytransmit the metadata to the DMNs. In other embodiments, the APIhandlers may transmit the metadata and policies directly to the DMNs ofthe appropriate cells. In some embodiments, an intermediary fleet of APIhandlers may not be required; instead, an AN of the IPPC may receiveclient-submitted administrative or control plane requests. The policiesmay, for example, indicate various aspects of the logic to be used togenerate packet processing actions for the applications—e.g., whichcombination of headers of received packets should be analyzed todetermine contents of headers of outbound packets, how the headercontents of outbound packets should be generated, how many outboundpackets are to be transmitted per received packet, etc.

After the metadata has been distributed, App1 packets may be permittedto start flowing from source endpoints to selected AINs (element 1510)(e.g., with the particular AIN used for a given packet of a group orflow being selected using a shuffle sharding technique of the kindintroduced above). ANs may start collecting metrics from AINs and DMNs,and may initiate cell reconfiguration/migration operations as and whenneeded—e.g., when some AINs/DMNs become unhealthy or unresponsive, orwhen the overall workload of C1 exceeds a threshold (which may occur dueto other applications to which C1 has been assigned).

A particular AIN of C1, AIN-k, may receive a packet from a sourceendpoint of App1 (element 1513). AIN-k may attempt to find (e.g., usinga key generated by applying a hash function to some combination of thepacket's headers or flow identifier) a corresponding action in a localaction cache in at least some embodiments. If an action for the packet(and other related packets of the flow) is found in the cache, asdetected in operations corresponding to element 1516, the action may beperformed by AIN-k (element 1519), resulting in one or more packetsbeing sent to one or more destination endpoints of App1. In some cases,depending on the manner in which source and destination endpoints areconnected to the various AINs of C1, AIN-k may be able to send thepackets to a destination endpoint without utilizing another AIN; inother cases, the outbound packets may be sent along a path that includesone or more other AINs of C1. The outbound packets may comprisetransformed versions of the received packet in some embodiments—e.g.,one or more header element values may be changed in the packetprocessing action.

If an action for the received packet is not found in the local cache atAIN-k (also via operations corresponding to element 1516), an actionquery may be transmitted to a selected DMN DMN-p of C1 from AIN-k in thedepicted embodiment (element 1522). DMN-p may be selected using any of anumber of techniques, such as flow-hashing, random selection,responsiveness of the different DMNs of C1 to health probes from AIN-k,and so on in different embodiments. DMN-p may use the propagatedapplication metadata and/or policy to generate the action in thedepicted embodiment, and provide a representation (e.g., an executablerepresentation) of the action to AIN-k. The action may for example beexpressed using instructions of an in-kernel register-based virtualmachine optimized for networking operations, such as eBPF or the like,in some embodiments. AIN-k may perform the received action and store itin its cache, from where it may be retrieved if/when additional relatedpackets are received at AIN-k in the depicted embodiment. Whenadditional packets arrive at any of the AINs, operations correspondingto elements 1513 onwards may be performed in various embodiments.

Virtual Traffic Hub Leveraging Packet Processing Service

A packet processing service of the kind introduced above may be employedfor a variety of applications in different embodiments. FIG. 16illustrates an example system environment in which a virtual traffic hubfor managing the flow of traffic between isolated networks using acell-based packet processing service may be implemented, according to atleast some embodiments. As shown, system 1600 may comprise a pluralityof isolated networks 1640, such as 1640A, 1640B, 1640C and 1640D, eachof which may comprise one or more computing devices with respectivenetwork addresses selected from a range of addresses selected for theisolated network. In at least some embodiments, the address ranges usedwithin one or more of the isolated networks 1640 may comprise privateaddresses that are not advertised by default outside the network. As aresult, a routing/forwarding intermediary may be needed to enablepackets to flow between resources of the different isolated networks insuch embodiments, and a scalable virtual traffic hub (VTH) 1602 may beestablished to help fulfill such connectivity requirements.Conceptually, a higher-level hub-and-spoke network may be constructedwith the isolated virtual networks 1640 in the roles of spokes, linkedto one another via the virtual traffic hub 1602. The VTH may be set upusing control plane and data plane resources of the packet processingservice (PPS) in the depicted embodiment—for example, the control planeof the PPS may be responsible for automatically adding data plane nodesas more isolated virtual networks are programmatically attached to theVTH, or as the amount of traffic from existing isolated virtual networksthat have been programmatically attached to the VTH increases. A virtualtraffic hub may be referred to as a virtual router or a virtual gatewayin some embodiments.

At a high level, a given instance of a VTH may comprise a set offast-path PPS resources 1610 (such as a collection of one or more actionimplementation nodes or AINs with respective action caches, similar tothe AINs discussed earlier), a set of slow-path PPS resources 1614 (suchas a collection of routing decision master nodes or DMNs, similar to theDMNs discussed earlier), and a set of routing/forwarding metadata ornetwork state information entries 1608 (e.g., forwarding informationbases or FIB entries, associated policies and the like) in variousembodiments. The routing/forwarding metadata 1608 may be employed todetermine and generate actions in accordance with the requirements of aclient of the PPS in the depicted embodiment. PPS control plane metadata1690 may, for example, indicate the mappings between various VTHinstances and the respective data plane resources (AINs, DMNS, etc.)assigned to the VTH instances in some embodiments. The term “routingdecisions layer” may be used to refer collectively to the DMNs assignedto a VTH in at least some embodiments, and the term “actionimplementation layer” may be used to refer collectively to the AINs. Theterm “routing action” may be used to refer to at least some of theactions (which may be as simple as forwarding packets, and in some casesmay include transforming/replicating packets in various ways beforeforwarding the packets) performed at the action implementation layer invarious embodiments. In some embodiments, at least some of the AINsand/or DMNs assigned to a VTH instance may be part of (e.g., implementedusing respective virtual machines of) an isolated virtual network of aprovider network. In at least some embodiments, individual ones of thehosts/servers used for AINs and/or DMNs may be utilized for multipleVTHs and/or multiple clients, e.g., a multi-tenant approach may be usedfor managing resources used for VTHs.

Based on its routing/forwarding metadata 1602, a VTH may not necessarilypermit network traffic to flow among all pairs of isolated networksattached to the VTH in at least some embodiments. For example, asindicated by arrows 1655A, 1655B, 1655C, resources in isolated network1640C may communicate with resources in each of the other three isolatednetworks 1640A, 1640B and 1640C in the depicted scenario of FIG. 15 viaVTH 1602. However, while resources in isolated network 1640B and 1640Dmay communicate with resources in each other (as indicated by arrow1655D) and with resources in isolated network 1640C via the VTH 1602,they may not communicate with resources in isolated network 1640A.Similarly, resources in isolated network 1640A may only communicate withresources in isolated network 1640C via the VTH 1602 in the depictedexample scenario. In effect, one or more routing domains (each with arespective routing table) may be generated and managed using the VTH1602, with traffic being routed only within the specific isolatednetworks that belong to a given domain, in accordance withdomain-specific metadata 1608 provided to the VTH in at least someembodiments. Note that connectivity among several different types ofisolated networks may be implemented using a single VTH instance 1602 inat least some embodiments. For example, in one scenario, isolatednetworks 1640C and 1640D of FIG. 16 may be a pair of isolated virtualnetworks (IVNs) of a virtualized computing service (VCS), eachcomprising resources located within data centers of a provider network.Isolated network 1640A may comprise a set of resources at a locationexternal to the provider network, such as a customer's data center,connected to the VCS via a VPN connection, while isolated network 1640Bmay also comprise a different set of external resources, connected tothe VCS via dedicated physical links of the kind discussed above. SomeVTH instances may be used for connectivity among a homogeneous set ofisolated networks (e.g., all IVNs within the provider network, allVPN-connected external networks, or all dedicated link-connectedexternal networks) in various embodiments, while others may be used forconnectivity among a heterogeneous set of isolated networks.

According to some embodiments, a system may comprise one or morecomputing devices of a packet processing service. The computing devicesmay include instructions that when executed on a processor cause thecomputing devices to obtain or receive one or more programmatic requeststo configure a virtual traffic hub (VTH) as an intermediary for networktraffic between a plurality of isolated networks. In response to theprogrammatic requests, metadata indicating a set of resources assignedto the VTH may be stored, e.g., in a control plane repository of theservice in various embodiments. The set of resources may include, forexample, at least a first action implementation node (AIN) and at leasta first routing decision master node (DMN). In some embodiments, anisolated packet processing cell (IPPC) of the kind introduced earliermay be assigned to the VTH. Network state information entries, such asFIB entries or the like, may be propagated to the DMNs assigned to theVTH in various embodiments, e.g., from the PPS control plane.

At the first AIN, a first executable action or directive may be obtainedfrom the first DMN, for example in response to an action query in thedepicted embodiment. The action may be generated for one or more packetsof a first network flow in some embodiments, where the first networkflow is distinguished from other network flows by one or more headerentries of at least one data packet received at the first actionimplementation node from the first isolated network. The firstexecutable action may be generated at the DMN based at least in part onthe network state information entries. In at least some embodiments, anindication of semantics of the first executable action may not beprovided to the AIN—that is, details of exactly what is being done inthe action may not be provided, and the action implementation node maysimply be responsible for quickly executing the action when a packetcorresponding to the action is received. In at least some embodiments,the executable action may be expressed using an instruction set of anin-kernel register-based virtual machine optimized for networkprocessing. The executable action may be stored in a flow-indexed cache(e.g., a cache in which a flow identifier may be used as the key toperform a lookup for an action) at the AIN. Based at least in part onimplementing the executable action at the first AIN, contents of one ormore packets of the first network flow may be transmitted on a pathwayto another isolated network from the first AIN in various embodiments.The pathway may, in some cases, include one or more other AINs in someembodiments. A number of programmatic interfaces (e.g., APIs,command-line tools, web-based consoles, graphical user interfaces andthe like) may be implemented to enable PPS clients to submit varioustypes of requests pertaining to VTHs, and to receive correspondingresponses in different embodiments. In at least some embodiments, equalcost multi-pathing (ECMP) techniques may be employed at a VTH, enablinghigh bandwidths of message traffic to be supported. In embodiments inwhich VTHs are established using a managed packet processing service ofthe kind described, clients of the service may not need to dedicate anyof their own resources (e.g., hardware routers or virtual machinesacquired by or allocated to the clients) to enable scalable routing ofnetwork packets between various isolated networks.

In at least one embodiment, a number of different metrics associatedwith a virtual traffic hub instance 1602 may be collected at the packetprocessing service, and provided on demand to clients, e.g., viaeasy-to-use visualization interfaces and/or other programmaticinterfaces. For example, for a given VTH hub, metrics collected andprovided may include the total number of inbound packets received duringa given time interval, the total number of outbound packets transmittedduring a given time interval, the total number of inbound packets forwhich outbound packets were not generated during a given time interval(e.g., either because routing/forwarding metadata for the inboundpackets was not provided to the VTH, or because clients have sentprogrammatic instructions to drop packets that meet specified criteria),and so on. In some implementations, rates of inbound, outbound anddropped packets, e.g., expressed in per-second units, may also orinstead be provided. In some embodiments, separate metrics may beprovided for the different causes of dropped packets—e.g., the number ofpackets that were dropped due to insufficient routing/forwardinginformation may be separated out from the number of packets that weredropped based on directive submitted by clients. In at least oneembodiment, the metrics may also be broken down by isolatednetwork—e.g., respective sets of metrics may be presented for each ofthe four isolated networks 1640A-1640D. In one embodiment, metricsaggregated for different categories of isolated networks—e.g., IVNswithin a provider network's VCS, versus networks connected via VPNs,versus networks connected via dedicated physical links—may be presented.In at least some embodiments, the provider network at which the packetprocessing service is implemented may implement a metrics service whichcan be used to obtain metrics about various other services of theprovider network, and the VTH-related metrics may be presented via sucha metrics service.

Customer Perspective Vs. Underlying Implementation

FIG. 17 illustrates examples of packet data paths between isolatednetworks connected via a virtual traffic hub, as viewed from a customerperspective and as implemented using a packet processing service,according to at least some embodiments. VTH instances 1710A and 1710B,similar in functionality to VTH 1602 of FIG. 16, may be set up on behalfof respective customers or clients C1 and C2 of a packet processingservice in the depicted example scenario. From the perspective 1702 ofthe customers, one programmatic request may, for example, be submittedto create a VTH instance, and another programmatic request may be usedto programmatically attach or associate an isolated network 1740 (e.g.,1740A, 1740B, 1740C or 1740D) to a specified VTH. In some cases, anotherprogrammatic request may be used to submit the routing/forwardingmetadata that is to be used to determine or generate actions for a givenrouting domain at a given VTH. After a VTH instance 1710 has beencreated, and the isolated virtual networks' logicalassociations/attachments 1720 (e.g., 1720A, 1720B, 1720C or 1720D) tothe VTHs have been performed, from the customer perspective traffic maybegin to flow among the isolated networks 1740 via the VTH, e.g., alonglogical data paths 1722A or 1722B. A customer may not necessarily bemade aware of the details of exactly how many nodes are being used atthe VTH instance, the paths along which packets are transmitted amongnodes of the packet processing service, and so on in some embodiments.In other embodiments, at least some of the details may be provided tothe customers, e.g., in response to programmatic requests.

Within the packet processing service, as indicated in the underlyingmulti-tenant AINs view 1705, a plurality of AINs 1730 (e.g., actionimplementation nodes 1730A-1730M belonging to a given isolated packetprocessing cell of the kind discussed earlier) may be assigned for eachof the two CTH instances 1710A and 1710B. A shuffle-sharding algorithmmay be used to identify, for a given flow, a subset of AINs 1730 to beused for packets of a given flow originating at a given isolated network1740. Thus, for example, for a given flow of packets transmitted fromisolated network 1740A to isolated network 1740B, any of three AINs1730A, 1730F and 1730L may be used to process inbound packets, whileAINs 1730C, 1730I or 1730G may be available for transmitting outboundpackets. Similarly, for another flow associated with customer C2'sisolated networks, AINs 1730B 1730J and 1730M may be usable for inboundpackets from isolated network 1740C as per shuffle-sharding alternatives1777, and AINs 1730B, 1730H and 1730J may be usable for outbound packetsto isolated network 1740D. A given packet of a flow from a sourceresource or endpoint of isolated network 1740A may, for example, beprocessed at AIN 1730A, and, as a result of an action implemented at AIN1730A, a corresponding forwarded packet may be sent from AIN 1730A alongpath 1772A to AIN 1730G and from AIN 1730G to a destination resource atisolated network 1740B in the depicted embodiment. In some cases, as inthe case of traversed data path 1772B, the AIN (e.g., 1730) thatreceives an inbound packet of a flow may be able to directly transmitthe corresponding outbound packet to the destination isolated network(1740D in the example associated with path 1772B), instead of usinganother intermediary AIN in various embodiments. As indicated in FIG.17, at least some AINs may be configured in a multi-tenant mode, for useon behalf of different customers' VTHs—e.g., AIN 1730F may be used forpackets associated with isolated network 1740A of customer C1, and forpackets associated with isolated network 1740C of customer C2. In someembodiments in which a cell comprising a plurality of AINs 1730 (or aplurality of DMNs) is assigned to more than one VTH instance, any of theAINs (or DMNs) of the cell may be used for any of the VTHs, dependingfor example on the shuffle sharding or other workload distributionalgorithms being used.

Hub Data Plane Node Elements

As mentioned earlier, a virtual traffic hub may be assigned a set of oneor more action implementation nodes and a set of one or more routingdecision master nodes in at least some embodiments. FIG. 18 illustratesan example of the management of virtual traffic hub-related packetprocessing workloads at an action implementation node of a packetprocessing service, according to at least some embodiments. In thedepicted embodiment, at least one virtual network interface 1852(similar to the trunk VNIs shown in FIG. 4) may be established for thenetwork traffic entering and exiting an AIN (action implementation node)execution device/platform 1830. For example, in some embodiments, theplatform 1830 may comprise a virtual machine implemented at avirtualized computing service of a provider network. The actionimplementation node itself may comprise an I/O manager 1827 and one ormore workers 1825 (e.g., 1825A, 1825B or 1825C) in the depictedembodiment. Note that control-plane and health-management-relatedoperations may also be performed by the I/O manager and the workers insome embodiments, as discussed earlier in the context of FIG. 14; FIG.18 is focused more on data plane operations.

The I/O manager 1827 may be referred to as a work distributor in atleast some embodiments, as it may be responsible for receiving packetsvia the virtual network interface 1852 and directing a given packet to aparticular worker 1825 for processing, with the worker being selectedfor example using a consistent, deterministic flow hashing algorithm1862 applied to a flow identifier associated with the packet. Input tothe flow hashing algorithm may include one or more flow identificationpacket header elements of the kind discussed earlier, e.g. in thecontext of FIG. 5. The deterministic flow hashing may represent oneexample of deterministic mapping functions that may be used to selectworkers 1825 for a given packet or flow in different embodiments. In atleast some embodiments, individual ones of the workers 1825 and/or theI/O manager 1827 may comprise one or more virtual cores or threads. Inat least some embodiments, a worker 1825 may comprise an executionengine for programs expressed in an instruction set of an in-kernelregister-based virtual machine optimized for network processing similarto eBPF. In other embodiments, such virtual machine instruction setexecution engines may not be employed. In some embodiments, each worker1825 may instantiate and/or use an associated per-worker flow-indexedaction cache, within which representations of executable actionsgenerated at the decision master nodes may be stored. When a packet isreceived at a worker 1825 from the I/O manager, the action for it may belooked up in the corresponding cache, and performed if a cache hitoccurs. If the action is not in the cache, the worker may indicate tothe I/O manager that a cache miss occurred, and an action query may besent from the I/O manager to a decision master node in at least someembodiments. In various embodiments, entries may be removed or evictedfrom the action caches based on various factors, such as usage timingrecords that indicate that a given action has not been performed forsome threshold amount of time. In at least some embodiments, locks orother concurrency control mechanisms may not be required to access theindividual caches, and/or to store/evict cache entries, e.g., becauseonly a single worker may be expected to access entries associated with agiven flow when deterministic mapping techniques of the kind discussedabove are used to select workers for handling flows.

As suggested by its name, the I/O manager 1827 may be responsible fordata plane input/output operations of the workers 1825 in the depictedembodiment—e.g., the I/O manager may act as an intermediary for messagesbetween an individual worker 1825 and other entities (including otherAINs, DMNs and the like). In at least some embodiments, a given worker1825 may not have to communicate directly with other workers at thedevice 1830; instead, all communications to/from a worker may flowthrough the I/O manager. In some embodiments, the workers and the I/Omanager may be implemented as part of the same program or application,e.g., a program implemented using the Data Plane Development Kit orDPDK.

In at least one embodiment, a virtual machine or execution device beingused for an AIN of a virtual traffic hub may have several differentvirtual network interfaces (VNIs) attached—e.g., one for traffic from/toisolated networks, and others for communication with DMNs, other AINs ofthe same cell, administration nodes and so on. In some embodiments, oneor more branch VNIs may be programmatically associated with a singletrunk VNI, and such branch VNIs may be used for communications withother AINs, DMNs etc.

FIG. 19 illustrates an example of the management of virtual traffichub-related packet processing workloads at a decision master node of apacket processing service, according to at least some embodiments. Inthe depicted embodiment, at least one virtual network interface 1952 maybe established for the network traffic entering and exiting a DMN(decision master node) execution device/platform 1930. For example, insome embodiments, the platform 1930 may comprise a virtual machineimplemented at a virtualized computing service of a provider network.The DMN itself may comprise an I/O manager 1927, one or more workers1925 (e.g., 1925A, 1925B or 1925C), a local copy of at least a portionof a route table 1926, and/or a route table synchronization manager 1966in the depicted embodiment.

As in the case of the I/O manager of an AIN, the I/O manager 1927 of aDMN may be referred to as a work distributor in at least someembodiments, as it may be responsible for receiving messages (e.g.,action queries corresponding to packets received at an AIN) via thevirtual network interface 1952 and directing a given message to aparticular worker 1925 for processing. In some embodiments, a DMN worker1927 may be selected at random from among the available workers at thedevice 1930, while in other embodiments, a worker may be selected forexample using a consistent, deterministic flow hashing algorithm. In atleast some embodiments, individual ones of the workers 1925, the routetable synchronization manager 1966 and/or the I/O manager 1927 maycomprise virtual cores or threads. In some embodiments, a worker 1925may comprise a code generator for programs expressed in an instructionset of an in-kernel register-based virtual machine optimized for networkprocessing similar to eBPF. In other embodiments, such code generatorsmay not be employed. In some embodiments, each DMN worker 1925 may haveaccess to a common or shared route table 1926, into which contents ofmetadata tables 1955 (e.g., managed by the packet processing controlplane), or information derived from such tables, may be stored by thesynchronization manager 1966. The synchronization manager 1966 may, forexample, update the route table 1926 using entries from cell-levelmetadata tables 1955 in some embodiments, ensuring that recent changesto routing/forwarding information provided by clients are reflected atthe DMN.

When an action query (comprising some indication of a packet for which acache miss occurred at an AIN) is received at a worker 1925 from the I/Omanager 1927, a corresponding route for the cache-miss-causing packetmay be looked up (e.g., using a longest prefix match (LPM) lookupalgorithm) in at least some embodiments. If the lookup 1933 succeeds, anexecutable version of an action to route the packet (and other packetsof the same flow, if any) may be generated at the worker 1925, and sentback, e.g., via the I/O manager 1927, to the AIN from which the actionquery was received. In some embodiments, if no route is found for thepacket, a default action (such as an action that results in dropping thereceived packet), or an error-handling action (such as sending an errormessage to the source endpoint from which the packet was received at theAIN) may be generated in some embodiments and sent to the AIN. The DMNI/O manager 1927 may be responsible for data plane input/outputoperations of the workers 1925 in the depicted embodiment—e.g., the I/Omanager may act as an intermediary for messages between an individualworker 1925 and other entities (including AINs and the like). In atleast some embodiments, a given worker 1925 may not necessarilycommunicate with other workers at the device 1930. In some embodiments,the DMN workers 1925 and the DMN I/O manager 1927 may be implemented aspart of the same program or application, e.g., a program implementedusing the Data Plane Development Kit or DPDK.

In at least one embodiment, a virtual machine or execution device beingused for a DMN of a virtual traffic hub may have several differentvirtual network interfaces (VNIs) 1952 attached. For example, one VNI1952 may be used for traffic from/to AINs, and others for communicationwith other DMNs of the same cell, administration nodes and so on.

Protocol for AIN-DMN Interactions

In some embodiments, an encapsulation protocol may be used forcommunications between AINs and DMNs assigned to a virtual traffic hub.Such a protocol may be used, for example, in embodiments in which theAINs and/or DMNs are implemented using respective virtual machines, eachof which may have one or more virtual network interfaces with respectiveIP addresses. In such an embodiment, encapsulation may be performed forthe AIN-to-DMN and DMN-to-AIN communications because the networkaddresses of the physical network interfaces at the hosts where theAINs/DMNs are instantiated do not match the addresses of the virtualnetwork interfaces attached to the AINs/DMNs. (Encapsulation may also beperformed, for similar reasons, during communications between sourcevirtual machines at isolated networks from which application packetsoriginate, and the AINs in at least some embodiments.)

FIG. 20 illustrates an example of a sequence of interactions between anaction implementation node and a decision master node, according to atleast some embodiments. Events at four types of entities are illustratedin the depicted example: the source endpoint 2002 at which a packet isgenerated and sent to a virtual traffic hub similar to that discussedabove, the AIN layer 2010 of the virtual traffic hub, the DMN layer 2015of the virtual traffic hub, and the destination endpoints 2020 to whichthe original packet was directed. Note that individual ones of theevents illustrated in FIG. 20 may take different amounts of time invarious embodiments, e.g., generating an executable action may takelonger than transmitting a message.

In an event labeled E1, an original packet OP (e.g., the very firstpacket of the flow) is generated and sent to the AIN layer 2010. Inevent E2, a cache miss occurs in the action cache of the AIN whichreceives OP, and an encapsulated version EOP of the received packet,representing an action query, is sent to a selected DMN at DMN layer2015. Note that for at least some applications, fairly large messagesmay be transmitted from sources 2002 to destinations 2020, so in atleast some cases it may not be straightforward or possible to add a lotof metadata (e.g., encapsulation headers, generated executable actionsetc.) to a message frame that includes the OP. Because the executableaction generated at a DMN itself may comprise a non-trivial number ofbytes (e.g., several hundred bytes or even a few kilobytes), the actionand the OP may be sent back to the requesting AIN in multiple messagesinstead of a single message in some embodiments.

Upon receiving the EOP, the DMN may extract the OP from the EOP, andobtain a flow identifier from the OP in the depicted embodiment as partof event E3. A longest prefix match (LPM) algorithm may be used to querya route table and/or a forwarding table to determine an action to beperformed for the OP, and an executable version of the action may begenerated (e.g., in the form of eBPF byte code) in some embodiments. Inevent E4, the action and the flow identifier may be sent back to the AINfrom which the action query was received in the depicted embodiment. Atthe AIN layer 2005, in event E5, the executable version of the actionmay be inserted into the local action cache in the depicted embodiment,e.g., using the flow identifier as a key for the cache entry.

In event E6, the EOP may be sent back to the AIN from which the actionquery was received in the depicted embodiment. Note that in at leastsome embodiments, AINs may be stateless, so no information may have beenretained at the AIN regarding the fact that it had sent an action queryfor the OP earlier. When the AIN receives the EOP, it may extract the OPand its flow identifier, look up the corresponding action in its cache(which has been inserted in event E5), and execute the action, resultingin forwarding of contents of the OP to a destination 2020 in thedepicted embodiment. Given a fixed MTU (maximum transmission unit) sizefor communications between the various layers, in at least someembodiments it may become possible to support larger OPs (and/or largerexecutable actions) by using separate messages to send the executableaction and the OP back to the requesting AIN, than may have beensupportable if a single message were sent back to the requesting AINfrom the DMN layer. In effect, in the example scenario shown in FIG. 20,two messages may be sent back in response to an action query—one whichcontains a representation of the action, and causes the AIN to store theaction in its cache, and a second message which is used by the AIN toretrieve the action from the cache and execute/perform the action. In atleast one embodiment, if the size of an executable action exceeds athreshold, the action may be split into a plurality of segments, andindividual ones of the segments may be sent back (e.g., along with theflow identifier and a token indicating whether additional segmentsremain for the flow identifier) from the DMN layer to the AIN layer.

Routing Examples

In at least some embodiments, starting from high-levelrouting/forwarding metadata provided by a client on whose behalf avirtual traffic hub (VTH) is established, filtered route tables may becreated at decision master nodes assigned to the VTH, which may takeinto account details such as subnet membership, availability containermembership and the like to choose the most actions for client-submittedpackets. FIG. 21, FIG. 22 and FIG. 23 collectively illustrate an exampleof the creation and use of filtered route tables at decision masternodes designated for a virtual traffic hub, according to at least someembodiments.

In the embodiment depicted in FIG. 21, an isolated packet processingcell (IPPC) 2150 has been assigned to a particular VTH which is to actas a network intermediary between resources distributed among threeisolated networks of a customer C1: isolated network 2140A whichcomprises a subnet C1S1, isolated network 2140B which comprises adifferent subnet C1S2, and isolated network 2140C which comprises athird subnet C1S3. The IPPC 2150 comprises at least twelve AINs 2130,six of which (2130A-2130F) are in a first availability container (AC)2131A, and the remaining six (2130H-2130M) are in a second AC 2131B.Subnets C1S1 and C1S2 are also established in AC 2131A, while subnetC1S3 is in AC 2131B. The six AINs in AC 2131A may be referred to asmembers of a sub-cell 2150-2131A of IPPC 2150 for the purposes of thediscussion regarding FIG. 21-FIG. 23, and the six AINs in AC 2131B maybe referred to as members of a sub-cell 2150-2131B.

Subnet C1S1 has an associated CIDR (Classless Inter-Domain Routing)block 192.168.1.0/24, subnet C1S2 has a CIDR block 10.10.1.0/24, andsubnet C1S3 has a CIDR block 21.12.1.0/24 in the depicted examplescenario. From the customer C1's perspective, the isolated networks2140A, 2140B and 2140C may simply be programmatically attached to theVTH to enable connectivity among them in the depicted embodiment. Withinthe packet processing service used for the VTH, specific pathways may beset up in various embodiments, e.g., using virtual network interfaces(VNIs), between individual isolated networks and respective subsets ofAINs. For example, each subnet may be programmatically associated withthree AINs within its own availability container in the depictedembodiment: subnet C1S1 with AINs 2130A, 2130C and 2130D, subnet C1S2with AINs 2130C, 2130E and 2130F, and subnet C1S3 with AINs 2130H, 2130Jand 2130M. In at least some embodiments, a respective VNI may be set upat an AIN for each subnet with which that AIN is associated—e.g., if agiven AIN is associated with three subnets, that AIN may have threeseparate VNIs established. Such VNIs may be referred to as branch VNIsin various embodiments. A branch VNI may represent a VNI that can beprogrammatically associated, with very little overhead, with a trunk VNIof the kind discussed earlier, to perform an additional level ofmultiplexing in some embodiments. For example, in some embodiments, atrunk VNI may have several associated private IP addresses, and at leastsome of the associated branch VNIs may be assigned individual ones ofthat set of associated private IP addresses.

A high-level route table 2148 may be provided to the control plane ofthe packet processing service at which the VTH is established forconnectivity between the three isolated networks shown in FIG. 21. Atthis level, the route table may simply indicate that if a destinationaddress of a packet belongs to one of the three CIDR blocks, it shouldbe routed to resources within one of the three corresponding subnets.From this high-level route table, a 2^(nd)-level route table 2149 whichtakes sub-cell information into account may be constructed in atransformation step 2199, e.g., at the control plane of the packetprocessing service and/or at a decision master node in the depictedembodiment. In this 2nd-level table 2149, the destination informationincludes a sub-cell identifier and the identifiers of specific virtualnetwork interfaces at each of the AINs which are associated with thesubnets. As shown, for example, the entry for CIDR 192.168.1.0/24indicates that the packets with destination addresses within that blockmay be routed via a VNI with identifier VNI-1 at AIN 2130A, a VNI withidentifier VNI-2 at AIN 2130C, or a VNI with identifier VNI-3 at AIN2130D.

In at least some embodiments, from this 2^(nd)-level route table, arespective filtered route table may be generated within the DMNs of eachsub-cell (the DMNs are not shown in FIG. 21-23 to avoid clutter), whichtakes the availability containers of the AINs into account. Examples ofsuch filtered route tables 2251A and 2251B are shown in FIG. 22. In thisversion of the route tables, the entries in the 2^(nd)-level route table2149 may be modified as follows: (a) for entries within the samesub-cell as the DMN where the filtering is being performed, the VNIidentifier information may be retained, and the sub-cell information maybe discarded and (b) for entries in a different sub-cell, the VNIinformation may be discarded and the availability container informationmay be included. These two types of changes may be made because, in atleast some embodiments, sub-cell or availability container informationmay not be required when communicating within a given availabilitycontainer. In contrast, in such embodiments, when communicating outsideone's local availability container, an identifier of the AIN (e.g., ahost identifier or address) may be used instead of a branch VNIidentifier. As shown, the filtered route tables 2251A and 2251Bgenerated in each of the sub-cells or availability containers may havedifferent entries derived from the same 2^(nd)-level table entry. Intable 2251A, generated in sub-cell 2150-2131A, the sub-cell oravailability container information in the first two entries (for CIDRs192.168.1.0/24 and 10.10.1.0/24, which are in the same availabilitycontainer) is removed, while the identifier of the availabilitycontainer is appended (e.g., using a notation equivalent to AIN2130H@AC2131B) for the entry which corresponds to a non-localavailability container. Conversely, in table 2251B, the VNI identifiersmay be retained only for the 21.12.1.0/24 entry, and availabilitycontainer identifiers (@AC2131A) of the remote availability containermay be appended to the AIN identifiers for the other two entries.

When determining or generating an action for a given packet flow, a DMNmay use filtered routing tables of the kind shown in FIG. 22 to try andselect the most efficient route. For example, a route that minimizes thenumber of transmissions across AINs by using branch VNIs within the sameAIN if possible may be preferred, and/or if such a route is notpossible, a route that minimizes crossing availability containerboundaries may be preferred in some embodiments. Table 2351 of FIG. 23shows three different example route resolutions that may be generated byDMNs, each corresponding to packets directed to the same destination192.168.1.100. The route resolution actions may vary based on theavailability container in which the actions are generated by a DMN (andwhich corresponding filtered table 2251A or 2251B is used at the DMN) inthe depicted embodiment. Thus, for example, for a flow of packets from10.10.1.1 to 192.168.1.100, if the action is generated at a DMN inavailability container 2131A in response to a query from AIN 2130C, abranch-VNI-to-branch-VNI route (VNI-4 to VNI-3) at AIN 2130C itself maybe selected, as indicated by the forwarding rule in the first row oftable 2351.

In contrast, if an action query for the same flow is received from AIN2130E, the filtered route table 2251A may indicate that AIN 2130E doesnot have a local branch VNI for reaching the destination, so a differentAIN (one of 2130A, 2130C or 2130D) may be used. As shown in the thirdrow of table 2351, AIN 2130C may be selected for an AIN-to-AIN routecorresponding to the flow, and a forwarding rule indicating that thepackets of the flow that are received at AIN 2130E should be sent to AIN2130C.

In the third example, shown in the middle row of table 2351, a routethat crosses availability container boundaries may be selected, e.g.,when a packet originating at 21.12.1.10 is to be directed to192.168.1.100, and a corresponding action query is generated from AIN2130H. In this scenario, the first row of filtered table 2251B may beused, and an AIN-to-AIN route with AIN 2130D may be selected for theflow.

Hub-Related Programmatic Interactions

As mentioned earlier, a packet processing service may implement avariety of programmatic interfaces to enable clients to submit requests,e.g., to establish instances of applications such as virtual traffichubs, make configuration changes to the hubs, and so on in at least someembodiments. FIG. 24 illustrates example virtual traffic hub-relatedcontrol plane programmatic interactions between a client and a packetprocessing service, according to at least some embodiments. In thedepicted embodiment, packet processing service (PPS) 2412, similar infeatures and functionality to PPS 102 of FIG. 1, may implement a set ofprogrammatic interfaces 2477, such as APIs, command-line tools,web-based consoles, graphical user interfaces and the like. In at leastsome embodiments, an API handler fleet 2478 may receive requestssubmitted via such interfaces, and may pass on internal versions of atleast some of the requests to various other components of the PPS 2412.Responses to the requests, generated by the other components, may beprovided back to the clients 2410 from the API handler fleet. The APIhandler fleet may itself be automatically scaled up and down, e.g.,independently of the scaling of the isolated packet processing cells ofthe PPS, by the control plane of the PPS in various embodiments as therate at which requests are submitted increases or decreases. In otherembodiments, a separate API handler fleet may not be used.

A client may submit a CreateVTH request via the programmatic interfaces2477 in the depicted embodiment, requesting the creation of a newinstance of a virtual traffic hub (VTH) of the kind introduced earlier.In response, one or more metadata records representing the new VTHinstance may be stored at the PPS control plane, and an identifier(VTHID 2415) of the VTH instance may be provided to the client in atleast some embodiments. In some embodiments, a number of targetedattributes of the VTH may be indicated in the CreateVTH request, such asthe rate at which data packets are expected to be processed at the VTH,response time targets for packet transmissions, and so on.

As mentioned earlier, a given VTH instance may be used to implementmultiple routing domains in some embodiments, with a given routingdomain represented internally at the PPS at least in part by ahigh-level routing table to be used to direct traffic between aparticular set of isolated networks. Thus, for example, routes betweenisolated networks IN1 and IN2 may be determined as part of theoperations associated with one routing domain RD1 managed using a VTHinstance VTH1, while routes between isolated networks IN3 and IN4 may bedetermined as part of the operations associated with a second routingdomain RD2 managed using the same VTH instance VTH1 in some embodiments.A CreateVTHRoutingDomain request 2417 may be submitted by a client 2410to establish a new routing domain associated with a specified VTH in theembodiment depicted in FIG. 17. In some embodiments, routing/forwardingmetadata to be used for the routing domain, such as entries of a routinginformation base (RIB), forwarding information base (FIB), routingtables and the like may be passed as a parameter of the request toestablish the routing domain; in other embodiments, the metadata may beprovided in separate programmatic interactions. In response, the PPS mayprovide an identifier of the routing domain (RoutingDomainID 2419) insome embodiments. In at least one embodiment, by default, a given VTHmay be associated with a single automatically created routing domain, soa separate request to create the first routing domain of the VTH may notbe required. In scenarios in which multiple routing domains areassociated with a given VTH instance, the VTH may be responsible fortransmitting contents of network packets between isolated networks ofindividual ones of the routing domains, without crossing routing domainboundaries in various embodiments.

In various embodiments, a client may submit a programmatic request,AttachIsolatedNetworkToRoutingDomain 2421, to associate a specifiedisolated network (e.g., identified using one or more virtual networkinterface identifiers to be used for communications between the isolatednetwork and the VTH) with a routing domain. The identifier of therouting domain may be included as a parameter of request 2421 in someembodiments. In one embodiment, if the VTH instance has only one routingdomain, the identifier of the domain may not be required. In response tothe attachment request 2421, additional metadata indicating that thespecified isolated network has been linked to the VTH instance may bestored at the PPS control plane in some embodiments, and an attachmentidentifier 2423 may be provided to indicate that the requestedattachment has been completed. After the attachment is complete, packetsmay be permitted to flow, e.g., via one or more virtual networkinterfaces, between the isolated network and the nodes of the VTH invarious embodiments. In at least one embodiment, poll mode drivers (suchas DPDK poll mode drivers, which do not require asynchronousnotifications and therefore result in lower processing overhead than atleast some other approaches for data transfers) may be used fortransferring the packets to AINs (e.g., to I/O managers of the kinddiscussed earlier). In at least some embodiments, the particularisolated network being attached may be configured at premises externalto the provider network data centers at which the PPS is implemented. AVPN connection or a dedicated physical link (“direct connect”) to theprovider network may be indicated (for example by identifying one ormore gateways set up for traffic with the external network) in theattachment request 2421 in some embodiments. In some embodiments,separate types of attachment request APIs may be supported for isolatedvirtual networks external to the provider network—e.g., anAttachIsolatedNetworkViaVPN API may be supported for the VPN scenario,and an AttachIsolatedNetworkViaDirectConnect API may be supported forattaching isolated networks connected to the provider network viadedicated physical links.

In different embodiments, the assignment of an isolated packetprocessing cell (IPPC) to the VTH instance may occur in response to thefirst attachment request 2421 for a routing domain, in response to arequest 2417 to create a routing domain, or in response to a request2414 to create the VTH instance. Thus, the particular request thattriggers the assignment of data plane resources (some collection ofaction implementation nodes and decision master nodes) may differ indifferent embodiments.

A programmatic DescribeVTHConfig request 2425 may be submitted by aclient 2410 to view various properties of the VTH in the depictedembodiment, such as the number of routing domains of the VTH, the numberand identifiers of different isolated networks attached to the routingdomains or the VTH, the number of data plane nodes at each layer, and soon. In response, the requested information may be provided via one ormore VTHConfigInfo messages 2427 in the depicted embodiment. In at leastone embodiment, a user-friendly graphical view of the configuration maybe provided.

Clients 2410 may submit ModifyVTHConfig messages 2429 of various typesin different embodiments to request changes to the configuration of aVTH. Such changes may, for example include modified/additional FIBentries or specific routes supplied by the client, changes to thepolicies being used to determine actions, changes in the number of AINsand/or DMNs being used (e.g., increasing the number of AINs/DMNs tohandle increased traffic levels), changes to availability or performancetargets for the VTH, and so on in different embodiments. The PPS controlplane may verify that the requested changes are acceptable with respectto the PPS's own policies regarding security, billing and the like, andmake the requested changes if they are found acceptable. A ModCompletemessage 2431 may be sent to the client to indicate that the requestedchanges have been performed in some embodiments.

In at least one embodiment, multiple VTH instances may be established onbehalf of a client (e.g., in different geographical regions), and aLinkVTHs request 2433 may be submitted by the client to establish anetwork path between a pair of VTH instances. Such a request may bereferred to as a hub linkage request in some embodiments. In response,the appropriate networking configuration changes may be implemented atthe PPS control plane, metadata indicating that a path between the pairof VTH instances has been configured/established may be stored, and aLinkComplete message 2435 may be sent to the client to indicate that thetwo VTH instances have been linked to enable traffic to flow betweenthem in the depicted embodiment. After such a hub linkage is completed,traffic may be routed/forwarded from one isolated network associatedwith a first VTH, through the second (linked) VTH, to a second isolatednetwork in various embodiments.

In some embodiments, one or more other types of VTH-related programmaticrequests, not shown in FIG. 24, may be submitted by clients 2410 andfulfilled at the PPS. For example, in one embodiment, a given VTHinstance may be shared among multiple client accounts, e.g., in responseto the equivalent of a ShareVTHWithAccounts(AccountsList) requestindicating the set of client accounts and the VTH instance to be shared.In some embodiments, an authorized client may programmatically accept orreject attachment requests submitted by other clients or users—e.g.,client C1 may establish a VTH, share the VTH with other clients orusers, and if/when an attachment request is submitted by one of theother clients or users, C1 may be sent a programmatic request to approveor reject the attachment of a specified isolated network to the VTH. Inone embodiment, programmatic requests for packet processing metrics ofthe kind discussed earlier (e.g., total number of inbound packetsreceived from one or more isolated networks at the VTH in some specifiedtime interval, total number of outbound packets sent from the VTH to oneor more isolated networks, total number of dropped inbound packets, andso on) may be supported. In at least one embodiment, at least some ofthe types of requests indicated in FIG. 24 and/or discussed above maynot necessarily be supported by the packet processing service.

Linked Hubs

In some embodiments in which the packet processing service at whichvirtual traffic hubs are established is implemented at a providernetwork, the resources of the provider network may be geographicallydistributed, e.g., among several geographical regions, with individualregions comprises respective sets of cities, states or countries. Someclients of such a packet processing service may also have respectiveisolated networks, either inside the provider network, or in externalpremises, in different geographical regions. In at least someembodiments, the packet processing service may support linking ofvirtual traffic hubs in response to client requests, e.g., to enabletraffic to be routed between isolated networks that are geographicallyfar apart. Hubs may also or instead be linked for other reasons, e.g.,based on preferences of clients that may wish to separate groups ofisolated networks and associated hubs for administrative purposes whilestill enabling traffic to flow among the groups.

FIG. 25 illustrates an example scenario in which multiple virtualtraffic hubs may be programmatically linked to one another, according toat least some embodiments. In the depicted embodiment, two VTHinstances, 2502A and 2502B, have been established on behalf of the samecustomer of a packet processing service similar to PPS 102 of FIG. 1.Isolated networks 2540A and 2540B have been programmatically associatedwith VTH 2502A, while isolated networks 2540C, 2540D and 2540E have beenprogrammatically associated with VTH 2502B. Isolated networks 2540A and2540B and VTH 2502A may, for example, be located in a differentgeographical region than isolated networks 2540C-2540E and VTH 2502B inthe depicted scenario, although such geographical separation may not berequired to link VTHs in at least some embodiments. In response to aprogrammatic request from a client, a hub-to-hub link 2572 may beestablished in the depicted embodiment, comprising for example some setof networking intermediary devices such as one or more routers, gatewaysor the like. The appropriate routing metadata may be propagated to theintermediary devices to enable data packets to flow along one or moremulti-VTH-pathways 2556 in the depicted embodiment. In some embodiments,the pathways may utilize high-speed dedicated physical links associatedwith a provider network. By setting up such VTH-to-VTH links in responseto client requests, the packet processing service may enable arbitrarilycomplex hub-and-spoke configurations to be set up in some embodiments,with resources in the spoke isolated networks of any given hub beingable to communicate efficiently and in a scalable manner with otherresources in spoke isolated networks of other hubs that may begeographically distant.

Methods for Supporting Virtual Traffic Hubs

FIG. 26 is a flow diagram illustrating aspects of operations that may beperformed to route traffic between isolated networks using a virtualtraffic hub that utilizes resources of a packet processing service,according to at least some embodiments. As shown in element 2601,metadata indicating that one or more AINs (action implementation nodes)and DMNs (decision master nodes) of a packet processing service havebeen assigned to a virtual traffic hub (VTH) instance which is to serveas a packet forwarding intermediary between a plurality of isolatednetworks may be stored, e.g., at a control plane of the service.Individual ones of the AINs and DMNs may be implemented using one ormore physical and/or virtual computing devices in different embodiments.In some embodiments, the packet processing service may be implemented aspart of a suite of services of a provider network that includes avirtual computing service (VCS), and one or more of the isolatednetworks may comprise respective isolated virtual networks set up onbehalf of VCS clients. Other isolated networks may comprise, forexample, networks on client-owned or client-managed premises, such asdata centers external to the provider network. The VTH instance may becreated, and the metadata indicating the assignment of the AINs and DMNsmay be stored, in response to one or more programmatic requests directedto the packet processing service in some embodiments. For example, inone embodiment one programmatic request may result in storage ofmetadata indicating that a new VTH has been created (without associatingthe VTH to any isolated network), and the metadata indicating theAIN/DMN assignments may be generated in response to a second request toattach one or more of the isolated networks to the VTH. As mentionedearlier, in some embodiments, a given VTH may be established for routingtraffic of several different routing domains. In some embodiments, atleast one isolated packet processing cell (IPPC) similar to the IPPCsshown in FIG. 1 may be assigned to the VTH.

As indicated in element 2604, network state information entries (e.g.,FIB entries) and/or routing/forwarding policies that can be used todetermine and/or generate packet processing actions for groups ofrelated packets originating at the isolated networks may be propagatedto the DMNs. In at least one embodiment, clients may provide routinginformation base (RIB) entries via programmatic interfaces to one ormore control plane components of the packet processing service at whichthe VTH is instantiated, and corresponding forwarding information base(FIB) entries may be generated from the RIB entries and included in thestate information provided to the DMNs. After the metadata has beenpropagated, in at least some embodiments packets may be allowed to flowfrom resources within the isolated networks to the AINs designated forthe VTH (element 2607).

A given AIN, AIN-k may receive a packet from some source endpoint withina given isolated network in the depicted embodiment (element 2610).AIN-k may, for example, be selected as the recipient of the packet basedon the use of flow hashing and/or shuffle-sharding algorithms in variousembodiments. AIN-k may attempt to look up a packet forwarding action tobe implemented for the received packet in a local cache, e.g., using aflow identifier of the packet as the lookup key in the depictedembodiment. If such an action is found in the cache, as detected inoperations corresponding to element 2613, the action may be performed atAIN-k, resulting in one or more outbound packets corresponding to thereceived packet being sent to one or more destinations in anotherisolated network associated with the VTH (element 2616). In some casesan outbound packet may be sent along a path that includes another AIN,while in other embodiments the path may not include any other AINs thanAIN-k itself.

If a representation of a forwarding action is not found in the cache,AIN-k may transmit an action query to a particular DMN (DMN-p) assignedto the VTH in the depicted embodiment (element 2619). DMN-p may use thenetwork state information entries and/or policies which were propagatedto the VTH's DMNs earlier to generate an executable packetprocessing/forwarding action and send the executable action to AIN-k. AtAIN-k the action may be cached and performed in various embodiments. Theaction may, for example, be expressed as a set of instructions of anin-kernel register based virtual machine optimized for networkingoperations in some embodiments. When/if the next packet is received atan AIN assigned to the VTH, operations corresponding to elements 2610onwards may be performed for the newly-received packet in variousembodiments.

As mentioned earlier, in at least some embodiments one or moreprogrammatic interfaces may be implemented by the packet processingservice. In response to programmatic requests submitted via suchinterfaces, a number of different administrative or control planeVTH-related operations may be performed (element 2622). For example,properties or metrics associated with the VTH (such as the rate at whichpackets are received from individual ones of the isolated networks, therate at which packets are forwarded to individual ones of the isolatednetworks, the resource utilization levels at various nodes of the VTH,and so on) may be provided in response to programmatic requests in someembodiments. In response to other types of requests, additional isolatednetworks may be attached programmatically to the hub, FIB entries and/orother metadata may be updated or provided to the packet processingservice for use at the VTH, the number of AINs/DMNs assigned to the VTHmay be changed, multiple VTHs may be linked, and so on in differentembodiments.

Handling Overlapping Private Address Ranges

In some embodiments, the isolated networks for which connectivity isenabled using virtual traffic hubs of the kind discussed above may eachhave one or more associated private network address ranges, from whichvarious addresses may be assigned to different resources (e.g., physicalor virtual machines) within the isolated networks. As suggested by theuse of the term “private” to describe such addresses, these addressesmay typically not be advertised outside the isolated networks, at leastby default. Because the address ranges are private, and may be selectedindependently by respective administrators or owners of the isolatednetworks, it may sometimes be the case that the address ranges of two ormore isolated networks overlap. In such scenarios, some form of addresstranslation may be required when communications among resources withpotentially identical addresses is enabled. In at least someembodiments, a virtual traffic hub may be configured to implement suchaddress translations, e.g., as part of the actions generated at therouting decisions layer of the hub and performed at the actionimplementation layer of the hub. In some embodiments, the appropriatetranslation rules/mappings to generate the actions may be provided by aclient. In at least one embodiment, the rules/mappings may be generatedautomatically within the VTH.

FIG. 27 illustrates an example system environment in which a virtualtraffic hub may be used to connect isolated networks which may haveoverlapping network address ranges, according to at least someembodiments. In system 2700, a virtual traffic hub (VTH) 2750 has beenestablished on behalf of a client, e.g., using the resources of a packetprocessing service similar to PPS 102 of FIG. 1, to enable networktraffic to flow from isolated network 2702B to isolated network 2702A,and also to enable network traffic to flow from isolated network 2702Cto isolated network 2702A. Isolated network 2702A may, for example,include some set of servers, such as email servers, file servers or thelike, to which service requests are directed from the isolated networks2702B and 2702C in the depicted embodiment. Isolated networks 2702B and2702C may have respective private network address ranges 2721A and2721B, which may potentially overlap with one another. Such overlaps mayexist, for example, because the networking configurations for theisolated networks may have been set up independently and at differenttimes (e.g., within different business or public-sector organizations,or within different units of the same organization). In some cases,isolated networks that have been in operation for years may be connectedat some point via VTHs such as VTH 2750, and it may not be practical tochange the set of private addresses being used within the isolatednetworks. Individual ones of the isolated networks 2702 may, forexample, comprise isolated virtual networks of a provider network,customer-premises networks external to the provider network, and so onin different embodiments.

In the depicted embodiment, the routing/forwarding metadata 2725 that isused to generate packet processing actions at the VTH (e.g., at decisionmaster nodes that employ a longest prefix match algorithm to look uprouting actions) may comprise a translation mapping 2757, which may beused to transform packet headers for packets originating at one of theisolated networks 2702B or 2702C, when transmitting the packets toisolated network 2702A. For example, consider a scenario in whichisolated network 2702B has a virtual machine VM1 with a private IPaddress 192.168.1.1, and isolated network 2702C also has a virtualmachine VM2 to which the same private IP address 192.168.1.1 has beenassigned. Packets from VM1, transmitted along path 2755 via VTH 2750,may be forwarded without modifying the sender's IP address in thedepicted embodiment. However, packets from VM2, being sent along path2756, may be modified by applying the translation mapping at the VTH2757 (e.g., changing the VM2 packets' sender IP address from 192.168.1.1to, say, 12.7.1.1) in the depicted embodiment. Similarly, at least someresponse packets sent back from isolated network 2702A to isolatednetwork 2702C may have their destination addresses translated byapplying the translation mapping in reverse (e.g., changing thedestination IP address from 12.7.1.1 to 192.168.1.1) in the depictedembodiment.

A translation mapping 2757 may indicate, for example, the specifictranslations or header transformations to be applied, and thesources/destinations (specified for example using the specific virtualnetwork interfaces that are used for VTH-to-isolated-network orisolated-network-to-VTH communications) whose packets are to betransformed in various embodiments. As a result of the translationtechniques implemented at the VTH, the internal networking configurationsettings of the isolated networks need not be modified in the depictedembodiment, thus simplifying the task of managing interconnectedisolated networks substantially. Note that at least in some embodiments,such translation techniques may be applied for packets flowing directlyamong pairs of isolated networks with overlapping address ranges, andnot just for the three-isolated-network scenario depicted in FIG. 27.For example, address translations may be performed at VTH 2750 forpackets flowing from isolated network 2702B to isolated network 2702C,and/or for packets flowing from isolated network 2702C to isolatednetwork 2702B in the depicted embodiment.

According to at least some embodiments, a system may comprise a set ofcomputing devices of a provider network. The computing devices mayinclude instructions that upon execution on a processor cause thecomputing devices to perform one or more configuration operations toenable connectivity, using a first virtual traffic hub (VTH), between aplurality of isolated networks including a first isolated network. Thefirst virtual traffic hub may comprise a plurality of layers including(a) a routing decisions layer at which respective routing action fornetwork packets are identified and (b) an action implementation layer atwhich routing actions identified at the routing decisions layer areperformed. In various embodiments, individual ones of the layers mayinclude one or more nodes of a packet processing service similar to thatdescribed above. The actions may be identified at the routing decisionslayer at least in part using, for example, metadata supplied by aclient, as well as a longest prefix match algorithm in at least oneembodiment. Respective network addresses may be assigned to one or moreresources of the first isolated virtual network from a first privateaddress range (e.g., a range of IP version 4 or IP version 6 addresses).

In at least one embodiment, a determination may be made, e.g., at one ormore nodes of the virtual traffic hub and/or at control plane elementsof the packet processing service being used for the virtual traffic hub,that the first private address range overlaps with (has at least oneaddress in common with) a second private address range of a secondisolated network. In different embodiments, the determination may bemade in response to various types of triggering events—e.g., when arequest to associate or attach the second isolated network to thevirtual traffic hub is received, or when a post-attach configurationchange is made at the second isolated network. An indication of atranslation mapping may be propagated to at least a first decisionmaster node (DMN) of the routing decisions layer in some embodiments.The translation mapping may be intended to be applied for at least aportion of the second private address range. From the first DMN, arepresentation of a first action which includes applying the translationmapping may be provided to one or more action implementation nodes(AINs) of the action implementation layer of the VTH. At a particularaction implementation node, the first action may be performed withrespect to a received packet from the second isolated network. This mayresult, for example, in forwarding of a modified version of the receivedpacket (which originated at a second resource within the first isolatednetwork) to a second resource outside the second isolated network (e.g.,at a third isolated network associated with the hub, or at the firstisolated network). The modified version of the received packet maycomprise one or more header elements changed using the translationmapping in at least some embodiments.

FIG. 28 and FIG. 29 collectively illustrate examples of alternativeapproaches for detecting and responding to overlapping address rangesamong isolated networks connected via a virtual traffic hub, accordingto at least some embodiments. In option A of FIG. 28, for example, aclient 2801 may include a translation mapping as a parameter in arequest (AttachIsolatedNetwork) to attach an isolated network (which hasan overlapping private address range with respect to some other isolatednetwork that is currently attached, or is going to be attached) to a VTHor a routing domain of a VTH. The AttachIsolatedNetwork request may, forexample, be submitted to the packet processing service 2802 as one ofthe steps of configuring a VTH, similar to the steps discussed earlier.The inclusion of the mapping parameter within the request may serve asan indication that the overlap exists in some embodiments. The packetprocessing service may provide a programmatic response 2804 indicatingthat the mapping is accepted in the depicted embodiment. In someembodiments, the packet processing service 2802 may perform a set ofvalidation or verification operations, e.g., to ensure that the providedmapping does not result in conflicts with other private IP addressranges of isolated networks associated with the VTH, before acceptingthe mapping.

In Option B of FIG. 28, a client 2801 may submit anAttachIsolatedNetwork request to the packet processing service 2802, andthe service may detect whether an overlap exists between the private IPaddress ranges configured at the to-be-attached isolated network andsome other isolated network which is already attached to the targetedVTH. If such an overlap is detected, the client 2801 may be notified,e.g., via an AddressOverlapDetected message 2809, which may includedetails of the overlapping address range in at least some embodiments.In response to the AddressOverlapDetected message 2809, the client mayprovide a translation mapping 2810, which may be stored as part of theVTH-related metadata at the packet processing service.

In Option C of FIG. 28, if/when the PPS 2802 receives a request 2821 toattach an isolated network and detects an address overlap, the servicemay generate a proposed or candidate translation mapping for theoverlapping range, and send that proposed mapping 2823 to the clientprogrammatically for approval. If/when the client approves the proposedcandidate mapping, the mapping may be propagated to the DMNs assigned tothe VTH and corresponding actions may begin to be generated and appliedin the depicted embodiment.

In another approach, illustrated in Option D of FIG. 29, prior torequesting an attachment of an isolated network, a client 2801 mayprovide an indication of a set of isolated networks that are to beconnected using a VTH to the PPS 2802, and request the PPS to detectaddress overlaps (e.g., via DetectAddressOverlaps message 2903). The PPS2802 may examine the networking configurations of the isolated networks,and if any overlaps among private IP addresses are detected, anindication of such overlapped address ranges may be providedprogrammatically to the client (e.g., via CurrentOverlappedRangesmessage 2904). The client 2801 may then submit attachment requests 2906indicating translation mappings to be applied with respect to theoverlapped ranges identified by the PPS in the depicted embodiment.

In Options A-D illustrated in FIG. 28 and FIG. 29, the client generatesand/or approves the translation mappings to be applied at the VTH. Insome embodiments, clients may wish to leave the details of detecting andgenerating address translation mappings entirely to the PPS, and may notnecessarily be interested in approving the mappings. In Option E of FIG.29, for example, a client may use an AutomateOverlappingAddressHandlingrequest 2908 to inform the PPS 2802 that address overlap detection andmanagement is to be fully automated, without requiring additional workfrom the client. In response, the PPS 2802 may send an acknowledgementmessage 2909 indicating that automated handling of overlapping addressranges has been initiated in the depicted embodiment. Subsequently, whenan isolated network is to be attached to a VTH on behalf of the client2801, the PPS 2802 may determine whether that isolated network has anyprivate address ranges that overlap with those of other attachedisolated networks. If such overlaps are detected, the PPS 2802 maygenerate a translation mapping and start using the mapping, e.g.,without additional interactions with the client 2801.

In at least some embodiments, the PPS 2802 may comprise a post-attachconfiguration change detector 2957, which may check whether any newaddress ranges have been configured or identified for use withinisolated networks that have already been associated with the VTH, and ifso, whether those new address ranges overlap with existing addressranges in use in other isolated networks associated with the VTH. Ifsuch overlaps are detected, corresponding new translation mappings maybe generated automatically and used in the depicted embodiment. Notethat such automated detection of post-attachment configuration changesmay be performed regardless of the particular option (Option A-Option Eof FIG. 28 and FIG. 29) being used to detect the address overlaps andgenerate/use the mappings in at least some embodiments.

If and when the client 2801 wishes to view translation mappings that arein use for their VTH, a ShowTranslationMappingslnUse request 2910 may besubmitted to the PPS 2802 in the depicted embodiment, and the currentset of in use mappings 2911 (including one or more attributes of themappings, such as when they were generated, the sources from which themappings were obtained, and the like) may be provided or displayed inresponse. Requests to display the mappings in use at a VTH may bereceived and fulfilled regardless of the particular option (OptionA-Option E of FIG. 28 and FIG. 29) that is used to detect the addressoverlaps and generate/use the mappings in at least one embodiment. Invarious embodiments, any of a variety of response actions may beundertaken if/when an address overlap is detected among one or morepairs of isolated networks connected via a hub—e.g., in some cases theoverlap response action may include notifying one or more clients thatan overlap exists, in other cases the response action may includeauto-generating a candidate mapping, etc. In at least some embodiments,prior to programmatically attaching/associating a given isolated networkto a hub, the PPS may verify that either (a) no overlaps exist betweenthe address ranges of the to-be-associated isolated network and othercurrently-attached isolated networks or that (b) if any such overlapsexist, corresponding translation mappings have been generated andpropagated to the decisions layer of the virtual traffic hub. Later, asand when configuration changes are made at one or more of the attachedisolated networks in such embodiments, new address range overlaps may insome cases be detected, and corresponding actions may be initiated bythe VTH. Other approaches towards detecting and responding to overlappedprivate address ranges than those shown in FIG. 28 and FIG. 29 may beemployed in some embodiments.

FIG. 30 is a flow diagram illustrating aspects of operations that may beperformed to route traffic between isolated networks using a virtualtraffic hub, in scenarios in which the isolated networks may haveoverlapping address ranges, according to at least some embodiments. Asshown in element 3001, configuration operations to enable connectivitybetween various isolated networks using a multi-layer scalable virtualtraffic hub (VTH) with a set of action implementation nodes (AINs) anddecision master nodes (DMNs) may be initiated or performed. The AINs andDMNs may be part of the data plane of a packet processing servicesimilar to PPS 102 of FIG. 1 in the depicted embodiment. A longestprefix match algorithm may be employed at the DMNs as part of theoperations performed to determine routing/forwarding actions to be takenfor various packets in some embodiments as discussed earlier. Individualones of the isolated networks may have respective private address rangesfrom which addresses are selected for and assigned to their resources.

A determination may be made that an overlap exists between a privateaddress range A-range of an isolated network IN-A that is associatedwith the hub, and a private address range B-range of another isolatednetwork IN-B in the depicted embodiment (element 3004). Such adetermination may be made, for example, when a programmatic request toattach IN-B to the hub is received, or when a configuration change ismade within IN-B which results in the selection or use of a new set ofaddresses. A translation mapping may be propagated to one or more of theDMNs in the depicted embodiment (element 3007), e.g., from the controlplane of the packet processing service. The mapping may, for example, beused to transform headers of packets associated with the overlappingportion of B-range and A-range when transmitting packets from one of theisolated networks with the overlapped range. In various embodiments, themapping may have been provided by a client on whose behalf the VTH wasset up, or may have been generated at the packet processing servicewhere the VTH is established. In at least some embodiments, the mappingmay be propagated prior to (e.g., as a pre-requisite) enabling trafficto begin flowing among at least some pairs of the isolated networks.

A DMN may provide a representation of an action TA that implements thetranslation mapping to an AIN, e.g., in response to an action queryresulting from an action cache miss at the AIN in at least someembodiments (element 3010). At the AIN, the TA action may be cached andperformed, resulting in the forwarding of one or more packets aftertheir headers have been modified based on the translation mapping in thedepicted embodiment (element 3013). The cached TA may be performed atthe AIN for additional packets of the same flow, e.g., without furtherinteractions with the DMN (element 3016). If/when new overlappingaddress ranges are set up within the isolated networks that have alreadybeen associated with the VTH, or if/when new isolated networks withoverlapping address ranges are attached, translation mappings for theadditional overlapping ranges may be generated and propagated to theDMNs, where they may be used to generate additional actions forexecution at the AINs in the depicted embodiment.

Automated Propagation of Routing Metadata Between Isolated Networks

In some embodiments in which a virtual traffic hub is uses to provideconnectivity between isolated networks, some or all of the privatenetworks associated with the hub may have respectivewithin-isolated-network route tables that may be changed as needed,e.g., by administrators or by the clients on whose behalf the isolatednetworks have been set up. These route tables may be used, for example,to determine where to direct packets originating at resources such asvirtual or physical machines within the isolated networks—e.g., whethera given packet should be sent to a virtual traffic hub, or sent to aresource within the isolated network itself. When new routes are addedto such local route tables within a given isolated network, or existingroutes are modified or removed, the changes may potentially affect thetraffic that enters or leaves the isolated network via the hub—e.g.,local route tables within other isolated networks may not have theentries needed to allow packets to be transmitted using the correctupdated routing information. Even after a virtual traffic hub with theappropriate forwarding information base is connected to an isolatednetwork IN1, in at least some embodiments traffic may not necessarilybegin to flow from resources within the isolated network to the hubuntil the appropriate entries (e.g., identifying paths to resources inother isolated networks IN2, IN3 etc. via the hub) are added to theIN1's own internal route tables.

In at least one embodiment, a virtual traffic hub may be configured to(e.g., in addition to performing the kinds of operations discussedearlier) automatically propagate local routing metadata between isolatednetworks, e.g., to enable the local routers within the isolated networksto start directing traffic to/from the virtual traffic hub. FIG. 31illustrates an example system environment in which a virtual traffic hubmay be used to automatically propagate routing information amongisolated networks, according to at least some embodiments. As shown,system 3100 may include a plurality of isolated networks (INs) 3102,such as 3102A, 3102B and 3102C, programmatically attached to a virtualtraffic hub (VTH) 3150 implemented using resources of a packetprocessing service similar to PPS 102 of FIG. 1. Individual ones of theisolated networks may have their own routing tables in the depictedembodiment, which may be referred to as IN-level routing tables, such astable 3105A at IN 3102, table 3105B at IN 3102B, and table 3105C at IN3102C. These IN-level routing tables may be modified independently ofone another, e.g., as new resources are configured or decommissionedwithin the individual isolated networks. As shown, VTH 3150 may comprisea set of hub-level routing metadata 3121 as well as a routing tableentry propagation manager 3122 in the depicted embodiment. The hub-levelrouting metadata 3121 may be generated and/or stored based on inputprovided by clients via APIs of the kind discussed earlier (e.g., APIswhose parameters include forwarding information base entries, or routinginformation base entries that may be converted to forwarding informationbase entries) in the depicted embodiment. In some embodiments, one ormore of the INs 3102 may comprise isolated virtual networks set up at avirtualized computing service (similar to isolated virtual networksdiscussed for example in the context of FIG. 3). In at least oneembodiment, at least some of the nodes of the VTH 3150, e.g. at therouting decisions layer or the action implementation layer, may beimplemented using resources of a provider network, while one or more ofthe resources used for a given isolated network 3102 may be external tothe provider network, e.g., at a customer premise.

The propagation manager 3122 may be responsible for intelligentlypropagating changes made at a given IN-level routing table 3105 of agiven isolated network to the appropriate set of other IN-level routingtables within other isolated networks in the depicted embodiment. Forexample, as indicated by arrows 3166A and 3166B, changes made toIN-level routing table 3105B may be propagated to tables 3105A and3105B. In at least some cases, the entries introduced into the remoteIN-level routing tables (e.g., 3105A or 3105B in the above example) maynot be copies of the entries in the source IN-level routing table (e.g.,3105C)—instead, a transformed version of the source entry (generatedusing an address translation mapping), or a new entry which takes theavailable paths to/from the VTH 3150 into account, may be inserted intothe remote IN-level routing tables. In a more general sense, the VTH3150 may be responsible for propagating updated routing-relatedinformation (as opposed to necessarily copying contents of route tableentries) as needed among its associated isolated networks in thedepicted embodiment. The decision to propagate the routing informationmay be made, for example, when an update is detected to analready-attached isolated network's routing table, and/or when a requestto attach a new isolated network to the VTH 3150 is received in variousembodiments. The propagation manager 3122 may utilize various types ofapplication programming interfaces and programmatic requests supportedat the isolated networks 3102 in some embodiments to obtain/inspectcontents of IN-level routing tables, to be notified when changes aremade to such IN-level routing tables, and so on, in the depictedembodiment.

According to some embodiments, a system may comprise a set of computingdevices of a provider network. The computing devices may includeinstructions that upon execution on a processor cause the computingdevices to store metadata indicating that a virtual traffic hub isconfigured as an intermediary for network traffic between a firstisolated network and a second isolated network. The first isolatednetwork may have an associated first routing table, and the secondisolated network may have its own associated second routing table in atleast some embodiments. The virtual traffic hub may comprise a pluralityof layers including (a) a routing decisions layer at which a routingaction for a network packet may be determined and (b) an actionimplementation layer at which routing actions identified at the routingdecisions layer may be performed in at least some embodiments. In atleast some embodiments, the actions may be determined at the routingdecisions layer based at least in part on employing a longest prefixmatch algorithm to look up an entry in a set of routing/forwardingentries. The computing devices may determine that at least a first entryof the first routing table is to be represented in the second routingtable, e.g., to enable network packets originating at one or moreresources of the second isolated network to be transmitted via thevirtual traffic hub to one or more resources of the first isolatednetwork in some embodiments. The computing devices may cause a new entrycorresponding to the first entry may be included in the second routingtable in such embodiments. Based at least in part on the new entry, anetwork packet originating at a first resource of the second isolatednetwork may be transmitted to an action implementation node of thevirtual traffic hub in various embodiments, and a routing action may beperformed at the action implementation node, resulting in a transmissionof contents of the network packet along a path to one or more resourcesof the first isolated network.

The propagation of routing information from one isolated network toanother via a virtual traffic hub may be triggered by any of severaltypes of events in different embodiments. FIG. 32 illustrates examplesof triggering events that may lead to the propagation of routinginformation by a virtual traffic hub to one or more isolated networks,according to at least some embodiments. The reception of an attachmentrequest (AttachIsolatedNetwork) 3203 via a programmatic interface at thepacket processing service control plane 3202 may represent one type ofevent that leads to route table entry propagations 3204. For example,the control plane of the packet processing service at which the hub isimplemented may issue a set of route detection APIs to obtain entries inthe IN-level routing tables of the to-be-attached isolated network, andpropagate corresponding entries to the IN-level routing tables of theother networks of the routing domain in the depicted embodiment.Similarly, in at least some embodiments, new entries may be added to theIN-level routing table of the to-be-attached isolated network as aresult of the issuance of APIs by the control plane 3202.

In a second type of triggering event, post-attachment routing tableentry changes 3213 at a given isolated network may be detected by thepacket processing service control plane 3202. In some embodiments, anautomated notification mechanism or API may be used by the control plane3202 to detect when changes to IN-level routing tables occur, while inother embodiments the control plane 3202 may periodically check forupdates to the IN-level routing tables using route-related APIs orrequests of the isolated networks. If/when the changes are detected,corresponding entries 3214 may be propagated to the appropriate set ofother isolated networks in the depicted embodiment.

As mentioned earlier, several different routing domains, each comprisinga plurality of interconnected isolated networks, may be set up using avirtual traffic hub in at least some embodiments. The automatedpropagation of routing information may be performed taking domainboundaries into account in at least some embodiments. FIG. 33illustrates examples of a domain-restricted propagation of routinginformation by a virtual traffic hub, according to at least someembodiments. In the depicted embodiment, two routing domains may be setup using a virtual traffic hub 3350 similar in functionality to the VTHsintroduced above: domain 3355A (comprising an interconnected group 3327Aof isolated networks 3301A, 3302B and 3302C) and domain 3355B(comprising a different interconnected group 3327B of isolated networks3301D and 3302E). The VTH may store separate hub-level routing domainmetadata 3356A and 3356B (e.g., including respective FIBS or RIBs) forrespective routing domains 3355A and 3355B in the depicted embodiment.Individual ones of the isolated networks 3302A-3302E may have theirrespective IN-level routing tables 3305A-3305E.

As indicated by arrows 3366A-3366D, the routing table entry (RTE)propagation manager 3322 of the VTH 3350 may propagate RTEs along pathsthat do not cross domain boundaries in the depicted embodiment. Thus,routing information may be propagated between isolated networks 3302Aand 3302B (arrow 3366A), between isolated networks 3302A and 3302C(arrow 3366C) and between isolated networks 3302B and 3302C (arrow3366B), but not from any of the isolated networks of group 3327A to anyof the isolated networks of group 3327B in the depicted embodiment.Similarly, within domain 3355B routing information may be propagatedbetween INs 3302D and 3302E (arrow 3366D), but routing information ofgroup 3327B may not be passed on to any of the isolated networks ofdomain 3355A. The routing domain metadata 3356 may be examined by theRTE propagation manager 3322 in at least some embodiments to determinewhere routing information from a given isolated network 3302 is to bepropagated. For example, if a request to attach another isolated network3302F to domain 3355 is received, in some embodiments the propagationmanager 3322 may consult the domain metadata 3356B and determine thatrouting information of to-be attached isolated network 3302F is to bepropagated among INs 3302D and 3302E, and not among other isolatednetworks of other domains (such as INs 3302A-3302C).

In various embodiments, as discussed earlier, private network addressranges of different isolated networks may overlap in some cases. In suchembodiments, when propagating routing information from one isolatednetwork to another, an address translation mapping may be used for theoverlapping portions of the address ranges. FIG. 34 illustrates anexample of the use of an address translation mapping during thepropagation of routing information by a virtual traffic hub, accordingto at least some embodiments. In the depicted embodiment, a virtualtraffic hub 3450 is configured as a routing intermediary betweenisolated networks (INs) 3402A and 3402B. Isolated network 3402A hasIN-level routing table 3405A, while isolated network 3402B has its ownIN-level routing table 3405B. A private network address range 3421A ofisolated network 3402 overlaps with a private network address range3421B of isolated network 3402B. As a result of the overlap, someentries in table 3405A may contain addresses that are already assignedto resources in IN 3402B, and vice versa.

In the embodiment depicted in FIG. 34, the routing table entrypropagation manager 3422 of the VTH 3450 may utilize an addresstranslation mapping 3423 to transform at least a portion of one or moreentries 3466 propagated from IN 3402A to IN 3402B. In some embodiments,the translation mapping 3423 may be generated automatically at the VTH3450, while in other embodiments, a client may provide the translationmapping 3423. Generally speaking, any of the approaches towardsdetecting overlapping private address ranges and obtaining correspondingtranslation mappings discussed earlier, e.g., in the context of FIG. 28and FIG. 29, may be employed in embodiments in which routing informationpropagation includes address translation as in the example scenariodepicted in FIG. 34. In response to determining that an overlap existsof the kind indicated in FIG. 34, the VTH or the packet processingservice may initiate one or more overlap response actions in variousembodiments. Such actions may include, for example, providing anindication of the overlap via a programmatic interface (e.g., to aclient or a network administrator), generating or obtaining thetranslation mapping 3423 and applying it to modify routing informationpropagated to one or both of the isolated networks involved, and so on.In at least one embodiment, an indication of the specific overlapresponse actions to be performed if/when such an overlap is detected maybe obtained via a programmatic interface—e.g., the client on whosebehalf the VTH is set up may provide a directive indicating the specifictype of response to be undertaken for address overlaps. In someembodiments, a client may indicate programmatically that the detectionof overlaps and/or responses to such overlaps are to be fully automated,e.g., without requiring additional interactions with the client, inwhich case the packet processing service may generate the translationmapping 3423 and use it to modify propagated routing information.

FIG. 35 is a flow diagram illustrating aspects of operations that may beperformed at a virtual traffic hub to propagate routing informationbetween isolated networks, according to at least some embodiments. Asshown in element 3501, configuration operations to enable connectivitybetween a plurality of isolated networks such as IN-A and IN-B using amulti-layer scalable virtual traffic hub (VTH) may be performed in thedepicted embodiment, and metadata indicating the establishment of theconnectivity may be stored. The VTH may be implemented using a packetprocessing service similar to PPS 102 shown in FIG. 1, and may comprisea set of action implementation nodes (AINs) of an AIN layer and somenumber of decision master nodes (DMNs) at a decisions layer. In at leastsome embodiments, the DMNs may identify or generate actions to beperformed at the AINs for various packets or packet flows, and theoperations performed at the DMNs may include utilizing a longest prefixmatch algorithm. The isolated networks connected via the VTH may havetheir respective routing tables, which may for example be used fortransmitting packets within the isolated networks (or to the VTH fromthe isolated networks) in the depicted embodiment. In the above examplescenario, IN-A may have its own routing table RT-A, and IN-B may haveits own routing table RT-B. Changes to these isolated-network-levelrouting tables may be made independently in at least some embodiments,e.g., based on changes to the set of resources deployed/configured inthe isolated networks. Note that at least in some embodiments, the VTHitself may maintain a hub-level routing table and/or otherrouting/forwarding metadata, e.g., for each routing domain for which theVTH is configured as an intermediary between isolated networks.

A determination may be made, e.g., at a route information propagationmanager of the VTH or the packet processing service, that at least oneentry RTE-1 in one of the isolated-network-level routing tables (e.g.,RT-A of IN-A) is to be represented in another isolated-network-levelrouting table (e.g., RT-B of IN-B) (element 3504). Such a propagation ofrouting information may be needed, for example, to enable trafficoriginating at resources of the IN-B to send packets to resources withinIN-A. In some embodiments, only a subset of the routing table entries ofa given isolated network such as RT-A may have to represented bycorresponding entries in RT-B—e.g., some isolated-network-level routinginformation may not necessarily have to be shared with other isolatednetworks. In one embodiment, for example, a client may inform the packetprocessing service programmatically regarding which subsets of routetable entries whose information is not to be propagated outside a givenisolated network (or specifically which routing information is to bepropagated).

The routing information propagation manager, which may for example beimplemented using one or more computing devices of the packet processingservice's control plane, may cause a new entry NRTE-1 corresponding toRTE-1 to be stored in RT-B (element 3507) in the depicted embodiment.The new entry NRTE-1 may represent at least some of the information thatwas contained in RTE-1 in the depicted embodiment, but the informationmay not necessarily be expressed in the same way as it was in RT-A in atleast some embodiments—e.g., an address translation mapping may be usedto generate NRTE-1 in some cases, or an address of a virtual networkinterface associated with the VTH may be included in NRTE-1 instead ofan address internal to IN-A.

As a result of the insertion of NRTE-1, network packets originating atone or more resources within the isolated network at which NRTE-1 isinserted (e.g., IN-B) may get transmitted to an AIN of the VTH (element3510) in at least some embodiments. At the AIN, a routing actionidentified at a DMN may be performed, resulting in the forwarding ofcontents of the network packets to resources in the isolated networkwhose information was propagated (e.g., IN-A) in such embodiments. Ineffect, the automatic propagation of routing information by the packetprocessing service or the VTH may simplify the task of networkadministrators of the isolated networks in various embodiments, as theadministrators may not have to keep track of all the destinations towhich routing changes made locally have to be propagated to enabletraffic to flow as intended via the VTH.

Handling DNS Operations Using Virtual Traffic Hubs

In at some embodiments, a virtual traffic hub that is set up at least inpart to route traffic among resources at isolated networks usingclient-supplied forwarding/routing metadata may also perform other typesof networking-related operations, including for example providing DNS(Domain Name System) information. FIG. 36 illustrates an example systemenvironment in which a virtual traffic hub may participate in thedistribution of Domain Name System (DNS) information to resources ofisolated networks, according to at least some embodiments. As shown,system 3600 may comprise a virtual traffic hub (VTH) 3650 of a packetprocessing service similar to PPS 102 of FIG. 1. VTH 3650 may be set up,e.g., as a result of a set of configuration operations performed at thepacket processing service control plane in response to programmaticrequests from clients, to provide connectivity among resources of atleast two isolated network (INs) 3602A and 3602B in the depictedembodiment. The VTH 3650 may, for example, comprise several layersincluding a routing decisions layer with one or more decision masternodes (DMNs) similar to those discussed earlier, and an actionimplementation layer with one or more action implementation nodes (AINs)similar to those discussed earlier; the DMNs may determine the actionsto be implemented for various packet flows, e.g., usingforwarding/routing metadata, and the AINs may cache the actions andperform the actions when packets of the corresponding flows are receivedat the VTH. In at least some embodiments, any combination of thedifferent VTH features discussed earlier, including generating andexecuting optimized executable actions for forwarding data packets,providing address translations for data packets flowing among theisolated networks, propagating IN-level routing information from oneisolated network to another, and so on, may be implemented by VTH 3650in addition to providing DNS support of the kind discussed below.

The isolated networks (INs) 3602A and 3602B may each have a respectiveprivate IP address range 3621, such as ranges 3621A and 3621B, fromwhich addresses may be assigned to individual resources (such as virtualor physical machines) in the respective isolated network. Such privateIP address ranges may be selected, for example, by clients on whosebehalf the isolated networks are set up, independently for the differentisolated networks, and may in some cases overlap with one another. Forexample, in the embodiment depicted in FIG. 36, at least one address inrange 3621A of IN 3602A is also in range 3621B of IN 3602B. Furthermore,in at least some embodiments, as indicated in elements 3622A and 3622B,various resources in one or more of the isolated networks 3602 may havebeen assigned domain names (e.g., of the form “<xyz>.com”) that aremapped to respective private addresses from the ranges 3621. Each of theisolated networks may have its own DNS settings such as a respective setof one or more DNS server identifiers 3605 (e.g., 3605A or 3605B) in atleast some embodiments.

The VTH 3650 may comprise a DNS operations manager 3622 in the depictedembodiment, e.g., implemented using some combination of control planeand data plane components (e.g., DMNs and AINs) at one or more computingdevices. Any of several different modes of DNS support may be providedusing the VTH 3650 in different embodiments, as discussed below infurther detail. A set of VTH-specific DNS configuration metadata 3624may be stored in the depicted embodiment, indicating for example thespecific types of DNS message interceptions and/or transformations to beperformed, the additional DNS information sources (e.g., one or moremanaged DNS services implemented by a provider network) to be consulted,and so on. In at least some embodiments, a representation of an addresstranslation mapping 3623 may also be stored to enable overlappingaddress ranges to be handled, e.g., for straightforward routing purposesas well as for DNS messages.

In various embodiments, the DNS operations manager 3622 may determinethat a particular DNS message (e.g., a response 3666 to a DNS query 3667originating at one of the isolated networks 3602) that is directedtowards a resource R1 in one of the INs 3602 is to indicate a resourceR2 within one of the other INs (R1 and R2 are not shown in FIG. 36). R2may have a DNS name D1, for example, and a DNS query to obtain R2's IPaddress may have been submitted from R1. Furthermore, the operationsmanager 3622 may determine that within R2's IN, R2 is assigned a privateIP address IPAddr1 which falls within the overlapping private IP addressrange—thus, some other resource R3 in R1's IN may also potentially beassigned the same private IP address IPAddr1. Accordingly, in at leastsome embodiments, the operations manager 3622 may obtain (e.g., usingthe address translation mapping 3623) a different or translated versionTIPAddr1 of IPAddr1, and cause this modified version TIPAddr1 to beincluded, instead of IPAddr1, in the DNS message that is delivered toR1. In some embodiments, the translation mapping 3623 used to modify aDNS message may be provided by a client via a programmatic interface. Inother embodiments, the VTH may automatically detect overlapping privateIP address ranges as discussed above, and may automatically generate anaddress translation mapping to be used for DNS messages.

According to some embodiments, a system may comprise a set of computingdevices of a provider network. The computing devices may includeinstructions that upon execution on a processor cause the computingdevices to perform configuration operations to set up a virtual traffichub enabling connectivity between at least a first and second isolatednetworks, and store metadata indicating the hub and its associations.Individual ones of the isolated networks may have respective privatenetwork address ranges, from which respective addresses may be assignedto one or more resources (e.g., virtual machines, physical machinesetc.) of the isolated networks. In at least some embodiments, theprivate IP addresses of the different isolated networks associate withthe VTH may overlap with one another—e.g., at least one address in oneisolated network's address range may also be present in another isolatednetwork's address range. The virtual traffic hub may comprise aplurality of layers including (a) a routing decisions layer at which arouting action for a network packet may be identified/determined and (b)an action implementation layer at which routing actions identified atthe routing decisions layer may be performed in at least someembodiments. In at least some embodiments, the actions may be determinedat the routing decisions layer based at least in part on employing alongest prefix match algorithm to look up an entry in a set ofrouting/forwarding entries.

In various embodiments, the computing devices may determine that (a) aparticular domain name system (DNS) message, directed to a secondresource in the second isolated network, is to include an indication ofa first resource of the first isolated virtual network, and that (b) atthe first isolated network, the first resource is assigned a firstnetwork address within an overlapping private address range. Inresponse, the computing devices may obtain a transformed version of thefirst network address in at least some embodiments, and cause thetransformed version to be included in the particular DNS messagedelivered to the second resource. Using such an approach, the problem ofpotentially receiving a DNS response with an IP address which is sharedby a local resource (within the second isolated network), when theactual resource for which the query was generated is in another isolatednetwork and happens to be assigned the same IP address as the localresource, may be avoided in various embodiments.

As indicated earlier, DNS support may be provided in several differentways or modes via VTHs in some embodiments, with the particular modebeing indicated by a client of the packet processing services via one ormore programmatic interfaces. FIG. 37 illustrates examples ofprogrammatic interactions between a client and a packet processingnetwork at which a virtual traffic hub may be used to performDNS-related operations, according to at least some embodiments. Thepacket processing service at which VTHs are set up may implement avariety of programmatic interfaces in various embodiments, such as oneor more web-based consoles, a set of APIs, command line tools, graphicaluser interfaces and the like.

Three alternative options A, B and C for setting up VTH-based DNSsupport programmatically using such programmatic interfaces are shown byway of example in FIG. 37. In Option A, a client 3701 may, for example,submit a programmatic request 3703 (ShareDNSInfo) to the packetprocessing service (PPS) 3702, indicating that DNS information is to beshared among a specified list of isolated networks associated with agiven VTH in some embodiments. In effect, such a programmatic requestmay allow the packet processing service to start processing DNS requestsoriginating at individual ones of the isolated networks via the VTH. Thepacket processing service may store metadata indicating that automaticsharing of DNS information is to be implemented, and in at least someembodiments may provide an acknowledgement message 3704, indicating thatthe requested sharing of DNS information has been initiated. As part ofinternal operations to implement the requested sharing, in someembodiments routers within the isolated networks may be configured totransmit DNS requests to the VTH (e.g., to one of a set of AINs of theVTH), and executable actions to perform address translations when neededfor DNS hosts/resources with overlapping private IP addresses may begenerated at DMNs. As a result of storing the metadata indicating thesharing approach, DNS messages may be modified as discussed above tohandle overlapping IP addresses.

According to Option B, a special DNS endpoint (e.g., an IP addressassociated with a particular virtual network interface of the kinddiscussed earlier) may be established at the VTH, and the DNS serverssettings of the isolated network(s) may be set to point to that endpointin the depicted embodiment. For example, a client 3701 may submit aGetVTH-DNS-Settings request 3708 to the PPS 3702. The PPS 3702 mayprovide the DNS endpoint information, e.g., via VTH-DNS-EndpointInfomessage 3709 to the client. The client 3701 may then change an isolatednetwork's DNS settings, e.g., using a SetIsolatedNetworkDNSServermessage 3710 directed to the control plane 3702 of the isolated networkitself. As a result, metadata entries indicating that the VTH (via itsDNS endpoint) is to be used as a DNS server for requests originating inthe isolated network may be stored in the depicted embodiment. In someembodiments, the VTH may be used as the primary DNS server for theisolated network, while in other embodiments the VTH may be included asa non-primary DNS server, to which DNS queries may be directed only ifthe isolated network's primary DNS server is unable to resolve thequeries.

According to Option C of FIG. 37, a client 3701 may not necessarilychange DNS settings, but may instead simply submit anInterceptDNSResponsesAtVTH request 3721 via a programmatic interface tothe PPS 3702. Such a request may, for example, indicate that responsesto DNS requests from sources outside an isolated network are to beintercepted at the VTH, and modified as and when needed, e.g., to handleoverlapping private IP addresses in scenarios similar to those discussedearlier. In response, the PPS 3702 may store metadata indicating thatsuch interceptions are to be performed (e.g., using combinations of DMNsand AINs), perform one or more networking configuration operations atthe isolated networks associated with the VTH to cause at least a subsetof DNS messages to be directed to the VTH, and provide anacknowledgement message 3723 (DNSInterceptionInitiated) indicating thatthe requested types of interceptions have been begun in the depictedembodiment. Other types of programmatic interactions, not shown in FIG.37, may be employed in some embodiments to configure VTHs to performvarious types of DNS operations.

As discussed earlier, in at least some embodiments a packet processingservice used for instantiating VTHs may be implemented at a providernetwork. FIG. 38 illustrates an example use of a virtual traffic hub toprovide DNS information to isolated networks within and outside aprovider network, according to at least some embodiments. In thedepicted embodiment, provider network 3802 may comprise a plurality ofnetwork-accessible service, some of which may utilize other services—forexample, a managed DNS service 3810 and/or the packet processing service3850 may comprise virtual machines set up using the virtualizedcomputing service 3852. As discussed earlier, e.g., in the context ofFIG. 3, in at least some embodiments VTHs 3820, such as 3820A or 3820B,may be set up to process packets transmitted among a set of isolatedvirtual networks (IVNs), such as IVNs 3830A or 3830B established onbehalf of various clients of the virtualized computing service 3852.

In the depicted embodiment, isolated networks 3890, such as 3890A or3890B, set up at customer premises external to the provider network3802, may also be connected to each other (and to IVNs 3830) via theVTHs 3820. Generally speaking, any combination of isolated virtualnetworks 3830 of the VCS 3852 and/or external (e.g., customer-premise)isolated networks may be associated programmatically with a VTH such as3820A in the depicted embodiment, and DNS support may be provided viathe VTH to resources within any of the IVNs or external isolatednetworks. For example, hosts or virtual machines may be assigned domainnames mapped to private IP addresses in IVN 3830A, IVN 3830B,customer-premises isolated network 3890A, and/or customer-premisesisolated network 3890B in the depicted embodiment. The differentisolated networks associated with a given VTH 3820 may each have privateIP address ranges which may overlap with one another in at least someembodiments. DNS queries regarding the domain names being used forresources in any of the isolated networks shown may also originate atany of the isolated networks; e.g., a query for a domain name set up innetwork 3890A may originate at a resource in network 3890B or 3830A, anda query for a domain name set up in network 3830A may originate at aresource in network 3890A or 3830B. The VTH 3820A may determine when anIP address included in a DNS message directed to any of the isolatednetworks needs to be modified, e.g., to deal with overlapping IPaddresses in the manner discussed above, and apply the necessary addresstransformations to the DNS messages (e.g., DNS responses 3866A, 3866B,3866C or 3866D) in the depicted embodiment.

In at least some embodiments, one or more of the IP addresses includedin a DNS message may be obtained at a VTH 3820 from a managed DNSservice 3810 of the provider network. Such a managed DNS service 3810may, for example, be used by entities that host applications using theVCS 3852 for their own end-user customers, so that the end usercustomers can access the applications using domain names rather than IPaddresses. The managed DNS service 3180 may also interact seamlesslywith other parts of the computing infrastructure of the providernetwork, such as load balancing services, health management services andthe like to help with routing application requests to the appropriateVCS resources in at least some embodiments. In at least someembodiments, the managed DNS service may store DNS records for domainnames configured within various isolated networks, such as networks 3830and/or 3890. A VTH 3820 may act as a client of the managed DNS servicein some embodiments, and use information obtained from the managed DNSservice to prepare DNS responses to be provided to resources within theisolated networks. In other embodiments, the VTH 3820 may serve as anintermediary between the isolated networks and the managed DNS service.

FIG. 39 is a flow diagram illustrating aspects of operations that may beperformed at a virtual traffic hub to propagate DNS information toresources at isolated networks, according to at least some embodiments.As shown in element 3901, a set of configuration operations may beperformed, e.g., at a packet processing service similar to PPS 102 ofFIG. 1, to enable connectivity between a plurality of isolated networkssuch as IN-A and IN-B using a multi-layer scalable virtual traffic hubVTH1. VTH1 may, for example, be assigned a set of action implementationnodes (AINs) and decision master nodes (DMNs) as discussed earlier.Resources in IN-A and IN-B may be assigned addresses from potentiallyoverlapping respective private network address ranges in variousembodiments.

At VTH1, a determination may be made that a particular DNS messagedirected to a resource R1 in IN-B is to include an indication of aresource R2 of IN-A, and that the private address Addr1 assigned to R2is part of an overlapping address range (element 3904). A transformedversion of Addr1 may be generated or obtained at VTH1, e.g., using anaddress translation mapping that may have been provided by a client ormay have been produced at VTH1 (element 3907). VTH1 may cause thetransformed version of Addr1 to be included in the DNS response message(element 3910), and the DNS response message may be sent on to R1 in thedepicted embodiment (element 3913).

It is noted that in various embodiments, at least some operations otherthan those illustrated in the flow diagrams of FIG. 15, FIG. 26, FIG.30, FIG. 35 and/or FIG. 39 may be used to implement the packetprocessing-related and/or DNS-related techniques described above. Someof the operations shown may not be implemented in some embodiments ormay be implemented in a different order, or in parallel rather thansequentially.

Use Cases

The techniques described above, of using isolated packet processingcells to implement instances of various types of networking applicationssuch as virtual traffic hubs may be useful in a variety of scenarios. Asmore and more distributed applications are migrated to provider networkenvironments, especially environments in which isolated virtual networkscan be established for different clients, the need for efficient andfault-tolerant management of packet transformation operations is alsoincreasing. The clean separation of function between a fast actionimplementation layer and a decision making layer may simplify therollout of new functionality or additional nodes at the various layerswithout affecting the work being done at the other layers. A widevariety of client-selected customized packet processing operations,e.g., associated with Layer 3 of the Internet networking protocol stackor its equivalent in other protocol stacks, may be implementedefficiently using the described techniques, including for examplevirtual routing applications, multicast applications and the like.Clients of a packet processing service may not be required to deal withsuch problems as possible overlaps among private address ranges used inisolated networks, the propagating of route changes from one isolatednetwork to another, and/or the propagation of DNS information toresources within isolated networks. The overall responsiveness ofapplications that utilize the packet processing operations may beimproved, e.g., by quickly adding packet processing resources as theapplication workload increases. The security of networking applicationsmay be enhanced by isolating the set of resources utilized for a giveninstance of an application. Further, the user experience of systemadministrators and/or application owners may be improved by providingconfiguration information and metrics separately on aper-application-instance level.

Illustrative Computer System

In at least some embodiments, a server that implements a portion or allof one or more of the technologies described herein, including thevarious data plane and control plane components of packet processingservices and client-side devices that may interact programmatically withsuch services, may include a general-purpose computer system thatincludes or is configured to access one or more computer-accessiblemedia. FIG. 40 illustrates such a general-purpose computing device 9000.In the illustrated embodiment, computing device 9000 includes one ormore processors 9010 coupled to a system memory 9020 (which may compriseboth non-volatile and volatile memory modules) via an input/output (I/O)interface 9030. Computing device 9000 further includes a networkinterface 9040 coupled to I/O interface 9030.

In various embodiments, computing device 9000 may be a uniprocessorsystem including one processor 9010, or a multiprocessor systemincluding several processors 9010 (e.g., two, four, eight, or anothersuitable number). Processors 9010 may be any suitable processors capableof executing instructions. For example, in various embodiments,processors 9010 may be general-purpose or embedded processorsimplementing any of a variety of instruction set architectures (ISAs),such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitableISA. In multiprocessor systems, each of processors 9010 may commonly,but not necessarily, implement the same ISA. In some implementations,graphics processing units (GPUs) may be used instead of, or in additionto, conventional processors.

System memory 9020 may be configured to store instructions and dataaccessible by processor(s) 9010. In at least some embodiments, thesystem memory 9020 may comprise both volatile and non-volatile portions;in other embodiments, only volatile memory may be used. In variousembodiments, the volatile portion of system memory 9020 may beimplemented using any suitable memory technology, such as static randomaccess memory (SRAM), synchronous dynamic RAM or any other type ofmemory. For the non-volatile portion of system memory (which maycomprise one or more NVDIMMs, for example), in some embodimentsflash-based memory devices, including NAND-flash devices, may be used.In at least some embodiments, the non-volatile portion of the systemmemory may include a power source, such as a supercapacitor or otherpower storage device (e.g., a battery). In various embodiments,memristor based resistive random access memory (ReRAM),three-dimensional NAND technologies, Ferroelectric RAM, magnetoresistiveRAM (MRAM), or any of various types of phase change memory (PCM) may beused at least for the non-volatile portion of system memory. In theillustrated embodiment, program instructions and data implementing oneor more desired functions, such as those methods, techniques, and datadescribed above, are shown stored within system memory 9020 as code 9025and data 9026.

In one embodiment, I/O interface 9030 may be configured to coordinateI/O traffic between processor 9010, system memory 9020, and anyperipheral devices in the device, including network interface 9040 orother peripheral interfaces such as various types of persistent and/orvolatile storage devices. In some embodiments, I/O interface 9030 mayperform any necessary protocol, timing or other data transformations toconvert data signals from one component (e.g., system memory 9020) intoa format suitable for use by another component (e.g., processor 9010).In some embodiments, I/O interface 9030 may include support for devicesattached through various types of peripheral buses, such as a variant ofthe Peripheral Component Interconnect (PCI) bus standard or theUniversal Serial Bus (USB) standard, for example. In some embodiments,the function of I/O interface 9030 may be split into two or moreseparate components, such as a north bridge and a south bridge, forexample. Also, in some embodiments some or all of the functionality ofI/O interface 9030, such as an interface to system memory 9020, may beincorporated directly into processor 9010.

Network interface 9040 may be configured to allow data to be exchangedbetween computing device 9000 and other devices 9060 attached to anetwork or networks 9050, such as other computer systems or devices asillustrated in FIG. 1 through FIG. 39, for example. In variousembodiments, network interface 9040 may support communication via anysuitable wired or wireless general data networks, such as types ofEthernet network, for example. Additionally, network interface 9040 maysupport communication via telecommunications/telephony networks such asanalog voice networks or digital fiber communications networks, viastorage area networks such as Fibre Channel SANs, or via any othersuitable type of network and/or protocol.

In some embodiments, system memory 9020 may be one embodiment of acomputer-accessible medium configured to store program instructions anddata as described above for FIG. 1 through FIG. 39 for implementingembodiments of the corresponding methods and apparatus. However, inother embodiments, program instructions and/or data may be received,sent or stored upon different types of computer-accessible media.Generally speaking, a computer-accessible medium may includenon-transitory storage media or memory media such as magnetic or opticalmedia, e.g., disk or DVD/CD coupled to computing device 9000 via I/Ointerface 9030. A non-transitory computer-accessible storage medium mayalso include any volatile or non-volatile media such as RAM (e.g. SDRAM,DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc., that may be included in someembodiments of computing device 9000 as system memory 9020 or anothertype of memory. Further, a computer-accessible medium may includetransmission media or signals such as electrical, electromagnetic, ordigital signals, conveyed via a communication medium such as a networkand/or a wireless link, such as may be implemented via network interface9040. Portions or all of multiple computing devices such as thatillustrated in FIG. 40 may be used to implement the describedfunctionality in various embodiments; for example, software componentsrunning on a variety of different devices and servers may collaborate toprovide the functionality. In at least one embodiment, one or morenon-transitory computer-accessible storage media may comprise programinstructions that when executed on one or more processors cause one ormore computer systems (e.g., systems comprising one or more computingdevices similar to that shown in FIG. 40) to implement portions or allof the described functionality. In some embodiments, portions of thedescribed functionality may be implemented using storage devices,network devices, or special-purpose computer systems, in addition to orinstead of being implemented using general-purpose computer systems. Theterm “computing device”, as used herein, refers to at least all thesetypes of devices, and is not limited to these types of devices.

CONCLUSION

Various embodiments may further include receiving, sending or storinginstructions and/or data implemented in accordance with the foregoingdescription upon a computer-accessible medium. Generally speaking, acomputer-accessible medium may include storage media or memory mediasuch as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile ornon-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.),ROM, etc., as well as transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as network and/or a wireless link.

The various methods as illustrated in the Figures and described hereinrepresent exemplary embodiments of methods. The methods may beimplemented in software, hardware, or a combination thereof. The orderof method may be changed, and various elements may be added, reordered,combined, omitted, modified, etc.

Various modifications and changes may be made as would be obvious to aperson skilled in the art having the benefit of this disclosure. It isintended to embrace all such modifications and changes and, accordingly,the above description to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. A system, comprising: one or more computingdevices of a packet processing service of a provider network; whereinthe one or more computing devices include instructions that uponexecution on a processor cause the one or more computing devices to: inresponse to a programmatic request to configure a first virtual traffichub as an intermediary for network traffic between a plurality ofisolated networks, store metadata indicating (a) at least a first actionimplementation node assigned to the first virtual traffic hub, and (b)at least a first routing decision master node assigned to the firstvirtual traffic hub; propagate, to the first routing decision masternode, respective sets of state information entries for a first isolatednetwork; obtain, at the first action implementation node, a firstexecutable action from the first routing decision master node, whereinthe first executable action is to be implemented for one or more packetsof a first network flow, wherein the first executable action isgenerated at the first routing decision master node based at least inpart on the respective sets of state information entries, and wherein anindication of semantics of the first executable action is not providedto the first action implementation node; store, in a flow-indexed cacheof the first action implementation node, the first executable action;cause, based at least in part on implementing the first executableaction at the first routing action implementation node, contents of oneor more data packets of the first network flow to be transmitted to asecond isolated network.
 2. The system as recited in claim 1, whereinthe instructions upon execution on a processor cause the one or morecomputing devices to: generate, at the first decision master node, oneor more executable instructions of the first executable action using aninstruction set of an in-kernel register-based virtual machine optimizedfor network processing.
 3. The system as recited in claim 1, wherein thefirst action implementation node comprises a plurality of executionengines including a first execution engine, wherein the instructionsupon execution on the processor cause the one or more computing devicesto: instantiate, at the first action implementation node, respectiveflow-indexed caches corresponding to individual ones of the executionengines; utilize, at the first action implementation engine, adeterministic mapping function to determine that a first executionengine is to assigned to process packets of the first network flow,wherein input to the deterministic mapping function comprises one ormore flow identification packet headers, wherein the first executableaction is stored by the first execution engine in a correspondingflow-indexed cache without acquiring a lock, and wherein, upon obtaininga data packet of the first network flow, the first execution engineperforms a lookup operation in the first flow-indexed cache withoutacquiring a lock.
 4. The system as recited in claim 1, wherein a path tothe second isolated network comprises at least a second actionimplementation node.
 5. The system as recited in claim 1, wherein theinstructions upon execution on a processor cause the one or morecomputing devices to: obtain, via a programmatic interface, one or morerouting information base (RIB) entries associated with an isolatednetwork; generate, using the one or more routing information entries,one or more forwarding information base (FIB) entries; and transmit, tothe first routing decision master node, the one or more forwardinginformation base entries, wherein the one or more forwarding baseentries are included in the network state information entries.
 6. Amethod, comprising: performing, at one or more computing devices:storing metadata indicating (a) at least a first action implementationnode is assigned to a virtual traffic hub which is programmaticallyassociated with one or more isolated networks, and (b) at least a firstrouting decision master node is assigned to the first virtual traffichub; obtaining, at the first action implementation node, arepresentation of a first action from the first routing decision masternode, wherein the first action is to be implemented for a first networkflow, and wherein the first action is determined at the first routingdecision master node using state information of the one or more isolatednetworks; causing, based at least in part on performing the first actionat the first action implementation node, contents of one or more datapackets received from a first isolated network to be transmitted to asecond isolated network, wherein the one or more packets are part of thefirst network flow.
 7. The method as recited in claim 6, furthercomprising performing, by the one or more computing devices: in responseto an attachment request received via a programmatic interface, storingmetadata indicating that a first virtual network interface associatedwith the first isolated network has been programmatically attached tothe first virtual traffic hub, wherein at least one packet of the firstnetwork flow is directed to the first action implementation node via thefirst virtual network interface after the programmatic attachment iscompleted.
 8. The method as recited in claim 7, further comprisingperforming, by the one or more computing devices: utilizing a poll modedriver to obtain the at least one packet via the first virtual networkinterface.
 9. The method as recited in claim 6, further comprisingperforming, by the one or more computing devices: in response to a hublinkage request received via a programmatic interface, storing metadataindicating that a path between the first virtual traffic hub and asecond virtual traffic hub has been configured, wherein the secondvirtual traffic hub is associated with a third isolated network; andcausing, based at least in part on performing a second executable actionat the first action implementation node, contents of one or more datapackets received from the first isolated network to be transmitted to asecond action implementation node assigned to the second virtual traffichub.
 10. The method as recited in claim 6, further comprisingperforming, by the one or more computing devices: obtaining, via aprogrammatic interface, one or more entries of one or more of: (a) aroute table of the first isolated network or (b) a forwardinginformation base of the first isolated network; and propagating, to oneor more decision master nodes of the first virtual traffic hub,including the first decision master node, the state information of theone or more isolated networks, wherein the state information comprisesthe one or more entries.
 11. The method as recited in claim 6, furthercomprising performing, by the one or more computing devices: obtaining,via one or more programmatic interactions, an indication of a firstrouting domain and a second routing domain associated with the firstvirtual traffic hub, wherein the first routing domain includes the firstand second isolated networks, and wherein the second routing domainincludes a third isolated network and a fourth isolated network; andtransmitting contents of network packets between isolated networks ofindividual ones of the routing domains, without crossing routing domainboundaries.
 12. The method as recited in claim 6, wherein the firstaction implementation node is configured within a provider network, andwherein the first isolated network is external to the provider network.13. The method as recited in claim 6, wherein the representation of thefirst action comprises an executable program which is expressed in aninstruction set of an in-kernel register-based virtual machine optimizedfor network processing.
 14. The method as recited in claim 6, whereinthe first isolated network comprises a first isolated virtual networkestablished at a virtualized computing service of a provider network,and wherein the second isolated network comprises a second isolatedvirtual network established at the virtualized computing service. 15.The method as recited in claim 6, further comprising: in response to asecond programmatic request, modifying one or more of: (a) the number ofaction implementation nodes assigned to the first virtual traffic hub,or (b) the number of decision master nodes assigned to the first virtualtraffic hub.
 16. Non-transitory computer-accessible storage mediastoring program instructions that when executed on one or moreprocessors cause one or more computer systems to: store metadataindicating that (a) at least a first action implementation node isassigned to a virtual traffic hub which is programmatically associatedwith one or more isolated networks, and (b) at least a first routingdecision master node is assigned to the virtual traffic hub; obtain, atthe first action implementation node, a representation of a first actionfrom the first routing decision master node, wherein the first action isto be implemented for a first network flow, and wherein the first actionis determined at the first routing decision master node using stateinformation of the one or more isolated networks; cause, based at leastin part on performing the first action at the first actionimplementation node, contents of one or more data packets received froma first isolated network to be transmitted to a second isolated network,wherein the one or more packets are part of the first network flow. 17.Non-transitory computer-accessible storage media as recited in claim 16,wherein the program instructions when executed on one or more processorscause the one or more computer systems to: store, in a cache at thefirst action implementation node, an entry comprising (a) therepresentation of the first action and (b) a usage timing record of thefirst action; and remove, from the cache after the first action has beenperformed with respect to one or more data packets, the entry based atleast in part on a determination that the usage timing record indicatesthat the first action meets an eviction criterion.
 18. Non-transitorycomputer-accessible storage media as recited in claim 16, wherein thefirst action implementation node is instantiated at a first host,wherein the first virtual traffic hub is established on behalf of afirst client of a network-accessible service of a provider network,wherein the program instructions when executed on one or more processorscause the one or more computer systems to: instantiate, at the firsthost, a second action implementation node assigned to a second virtualtraffic hub, wherein the second virtual traffic hub is established onbehalf of a second client of the network-accessible service. 19.Non-transitory computer-accessible storage media as recited in claim 16,wherein the program instructions when executed on one or more processorscause the one or more computer systems to: transmit, from the firstaction implementation node in response to receiving a first packet ofthe first network flow, a first action query to the first routingdecision master node, wherein the first action query comprises at leasta portion of the first packet; transmit, from the first routing decisionmaster node to the first action implementation node in response to thefirst action query, a first message followed by a second message,wherein the first message comprises the representation of the firstaction, and wherein the second message comprises at least the portion ofthe first packet; store the representation of the first action in acache by the first action implementation node in response to receivingthe first message from the first routing decision master node; andretrieve, from the cache, the representation of the first action by thefirst action implementation node in response to receiving the secondmessage from the first routing decision master node.
 20. Non-transitorycomputer-accessible storage media as recited in claim 16, wherein theprogram instructions when executed on one or more processors cause theone or more computer systems to: provide, via a programmatic interface,one or more packet processing metrics of the virtual traffic hub,wherein the packet processing metrics include one or more of: (a) anumber or rate of packets received at the virtual traffic hub from oneor more isolated networks during a time interval, (b) a number or rateof packets transmitted from the virtual traffic hub to one or moreisolated networks during a time interval, or (c) a number or rate ofreceived packets for which no corresponding outbound packets weretransmitted from the virtual traffic hub during a time interval.